Interesting Programming facts about Fibonacci numbers

We know Fibonacci number, Fn = Fn-1 + Fn-2. 
First few Fibonacci numbers are 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, .... . 
Here are some interesting facts about Fibonacci number : 

1. Pattern in Last digits of Fibonacci numbers : 
Last digits of first few Fibonacci Numbers are : 

0, 1, 1, 2, 3, 5, 8, 3, 1, 4, 5, 9, 4, 3, 7, 0, 7, ... 

The series of last digits repeats with a cycle length of 60 (Refer this for explanations of this result). 

// C++ program to demonstrate that sequence of last
// digits of Fibonacci numbers repeats after 60.
#include <bits/stdc++.h>
using namespace std;

#define max 100

int main()
{
    long long int arr[max];
    arr[0] = 0;
    arr[1] = 1;
    int i = 0;

    // storing Fibonacci numbers
    for (i = 2; i < max; i++) {
        arr[i] = arr[i - 1] + arr[i - 2];
    }

    // Traversing through store numbers
    for (i = 1; i < max - 1; i++) {
        // Since first two number are 0 and 1
        // so, if any two consecutive number encounter 0 and
        // 1 at their unit place, then it clearly means that
        // number is repeating/ since we just have to find
        // the sum of previous two number
        cout << i << endl;
        if ((arr[i] % 10 == 0) && (arr[i + 1] % 10 == 1)) {
            break;
        }
    }
    cout << "Sequence is repeating after index " << i
         << endl;
}

// C program to demonstrate that sequence of last
// digits of Fibonacci numbers repeats after 60.
#include <stdio.h>
#define max 100

int main()
{
    long long int arr[max];
    arr[0] = 0;
    arr[1] = 1;
    int i = 0;

    // storing Fibonacci numbers
    for (i = 2; i < max; i++)
        arr[i] = arr[i - 1] + arr[i - 2];

    // Traversing through store numbers
    for (i = 1; i < max - 1; i++)
    {
      
        // Since first two number are 0 and 1
        // so, if any two consecutive number encounter 0 and
        // 1 at their unit place, then it clearly means that
        // number is repeating/ since we just have to find
        // the sum of previous two number
        if ((arr[i] % 10 == 0) && (arr[i + 1] % 10 == 1))
            break;
    }
    printf("Sequence is repeating after index %d", i);
}

// The code is contributed by Gautam goel (gautamgoel962)

// Java program to demonstrate that sequence of last 
// digits of Fibonacci numbers repeats after 60. 

class GFG{
static int max=100; 
public static void main(String[] args) 
{ 
    long[] arr=new long[max]; 
    arr[0] = 0; 
    arr[1] = 1;
    int i=0;

    // storing Fibonacci numbers 
    for (i = 2; i < max; i++) 
        arr[i] = arr[i-1] + arr[i-2]; 

    // Traversing through store numbers 
    for (i = 1; i < max - 1; i++) 
    { 
        // Since first two number are 0 and 1 
        // so, if any two consecutive number encounter 0 and 1 
        // at their unit place, then it clearly means that 
        // number is repeating/ since we just have to find 
        // the sum of previous two number 
        if ((arr[i] % 10 == 0) && (arr[i+1] % 10 == 1)) 
            break; 
    } 
    System.out.println("Sequence is repeating after index "+i); 
} 
}
// This code is contributed by mits

# Python3 program to demonstrate that sequence of last
# digits of Fibonacci numbers repeats after 60.


if __name__=='__main__':
    max = 100
    arr = [0 for i in range(max)]
    arr[0] = 0
    arr[1] = 1

# storing Fibonacci numbers
    for i in range(2, max):
        arr[i] = arr[i - 1] + arr[i - 2]

    # Traversing through store numbers
    for i in range(1, max - 1):
        

    # Since first two number are 0 and 1
    # so, if any two consecutive number encounter 0 and 1
    # at their unit place, then it clearly means that
    # number is repeating/ since we just have to find
    # the sum of previous two number
        if((arr[i] % 10 == 0) and (arr[i + 1] % 10 == 1)):
            break

    print("Sequence is repeating after index", i)

# This code is contributed by
# Sanjit_Prasad

// C# program to demonstrate that sequence of last 
// digits of Fibonacci numbers repeats after 60. 

class GFG{
static int max=100; 
public static void Main() 
{ 
    long[] arr=new long[max]; 
    arr[0] = 0; 
    arr[1] = 1;
    int i=0;

    // storing Fibonacci numbers 
    for (i = 2; i < max; i++) 
        arr[i] = arr[i-1] + arr[i-2]; 

    // Traversing through store numbers 
    for (i = 1; i < max - 1; i++) 
    { 
        // Since first two number are 0 and 1 
        // so, if any two consecutive number encounter 0 and 1 
        // at their unit place, then it clearly means that 
        // number is repeating/ since we just have to find 
        // the sum of previous two number 
        if ((arr[i] % 10 == 0) && (arr[i+1] % 10 == 1)) 
            break; 
    } 
    System.Console.WriteLine("Sequence is repeating after index "+i); 
} 
}
// This code is contributed by mits

<script>

// Javascript program to demonstrate that
// sequence of last digits of Fibonacci 
// numbers repeats after 60.     
var max = 100;

var arr = Array(max).fill(0);
arr[0] = 0;
arr[1] = 1;
var i = 0;

// Storing Fibonacci numbers
for(i = 2; i < max; i++)
    arr[i] = arr[i - 1] + arr[i - 2];

// Traversing through store numbers
for(i = 1; i < max - 1; i++) 
{
    
    // Since first two number are 0 and 1
    // so, if any two consecutive number encounter 0 and 1
    // at their unit place, then it clearly means that
    // number is repeating since we just have to find
    // the sum of previous two number
    if ((arr[i] % 10 == 0) && (arr[i + 1] % 10 == 1))
        break;
}

// Driver code
document.write("Sequence is repeating after index " + i);

// This code is contributed by gauravrajput1 

</script>

<?php
// php program to demonstrate that
// sequence of last digits of 
// Fibonacci numbers repeats after
// 60. global $MAX=100

    $arr[0] = 0;
    $arr[1] = 1;

    // storing Fibonacci numbers
    for ($i = 2; $i < 100; $i++)
        $arr[$i] = $arr[$i-1] +
                       $arr[$i-2];

    // Traversing through store
    // numbers
    for ($i = 1; $i <100 - 1; $i++)
    {
        // Since first two number are
        // 0 and 1 so, if any two 
        // consecutive number encounter
        // 0 and 1 at their unit place,
        // then it clearly means that
        // number is repeating/ since 
        // we just have to find the
        // sum of previous two number
        if (($arr[$i] % 10 == 0) && 
                ($arr[$i+1] % 10 == 1))
            break;
    }
    echo "Sequence is repeating after",
                         " index ", $i;

// This code is contributed by ajit
?>

Output: 

Sequence is repeating after index 60

Time complexity of the given program is O(max), as it runs two loops from 2 to max-1 and performs constant-time operations inside both loops. Hence, the time complexity is linear in terms of the value of max.

Space complexity of the program is O(max), as it creates an array of size max to store the Fibonacci numbers. The space required for other variables used in the program is constant and negligible compared to the array size. Therefore, the space complexity is also linear in terms of the value of max.

2. Factors of Fibonacci number : On careful observation, we can observe the following thing :

• Every 3-rd Fibonacci number is a multiple of 2
• Every 4-th Fibonacci number is a multiple of 3
• Every 5-th Fibonacci number is a multiple of 5
• Every 6-th Fibonacci number is a multiple of 8

Refer this for details. 

// C++ program to demonstrate divisibility of Fibonacci
// numbers.
#include<iostream>
using namespace std;
#define MAX 90

int main()
{
    // indexes variable stores index of number that
    // is divisible by 2, 3, 5 and 8
    long long int arr[MAX], index1[MAX], index2[MAX];
    long long int index3[MAX], index4[MAX];

    // storing fibonacci numbers
    arr[0] = 0;
    arr[1] = 1;
    for (int i = 2; i < MAX; i++)
        arr[i] = arr[i-1] + arr[i-2];

    // c1 keeps track of number of index of number
    // divisible by 2 and others c2, c3 and c4 for
    // 3, 5 and 8
    int c1 = 0, c2 = 0, c3 = 0, c4 = 0;

    // separating fibonacci number into their
    // respective array
    for (int i = 0; i < MAX; i++)
    {
        if (arr[i] % 2 == 0)
            index1[c1++] = i;
        if (arr[i] % 3 == 0)
            index2[c2++] = i;
        if (arr[i] % 5 == 0)
            index3[c3++] = i;
        if (arr[i] % 8 == 0)
            index4[c4++] = i;
    }

    // printing index arrays
    cout<<"Index of Fibonacci numbers divisible by"
           " 2 are :\n";
    for (int i = 0; i < c1; i++)
        cout<<" "<< index1[i];
    cout<<"\n";

    cout<<"Index of Fibonacci number divisible by"
           " 3 are :\n";
    for (int i = 0; i < c2; i++)
        cout<<"  "<< index2[i];
    cout<<"\n";

    cout<<"Index of Fibonacci number divisible by"
           " 5 are :\n";
    for (int i = 0; i < c3; i++)
        cout<<"  "<< index3[i];
    cout<<"\n";

    cout<<"Index of Fibonacci number divisible by"
           " 8 are :\n";
    for (int i = 0; i < c4; i++)
        cout<<" "<<index4[i];
    cout<<"\n";
}

// This code is contributed by shivanisinghss2110

// C program to demonstrate divisibility of Fibonacci
// numbers.
#include<stdio.h>
#define MAX 90

int main()
{
    // indexes variable stores index of number that
    // is divisible by 2, 3, 5 and 8
    long long int arr[MAX], index1[MAX], index2[MAX];
    long long int index3[MAX], index4[MAX];

    // storing fibonacci numbers
    arr[0] = 0;
    arr[1] = 1;
    for (int i = 2; i < MAX; i++)
        arr[i] = arr[i-1] + arr[i-2];

    // c1 keeps track of number of index of number
    // divisible by 2 and others c2, c3 and c4 for
    // 3, 5 and 8
    int c1 = 0, c2 = 0, c3 = 0, c4 = 0;

    // separating fibonacci number into their
    // respective array
    for (int i = 0; i < MAX; i++)
    {
        if (arr[i] % 2 == 0)
            index1[c1++] = i;
        if (arr[i] % 3 == 0)
            index2[c2++] = i;
        if (arr[i] % 5 == 0)
            index3[c3++] = i;
        if (arr[i] % 8 == 0)
            index4[c4++] = i;
    }

    // printing index arrays
    printf("Index of Fibonacci numbers divisible by"
           " 2 are :\n");
    for (int i = 0; i < c1; i++)
        printf("%d  ", index1[i]);
    printf("\n");

    printf("Index of Fibonacci number divisible by"
           " 3 are :\n");
    for (int i = 0; i < c2; i++)
        printf("%d  ", index2[i]);
    printf("\n");

    printf("Index of Fibonacci number divisible by"
           " 5 are :\n");
    for (int i = 0; i < c3; i++)
        printf("%d  ", index3[i]);
    printf("\n");

    printf("Index of Fibonacci number divisible by"
           " 8 are :\n");
    for (int i = 0; i < c4; i++)
        printf("%d  ", index4[i]);
    printf("\n");
}

// Java program to demonstrate divisibility of Fibonacci 
// numbers. 

class GFG
{
static int MAX=90; 

// Driver code
public static void main(String[] args) 
{ 
    // indexes variable stores index of number that 
    // is divisible by 2, 3, 5 and 8 
    long[] arr=new long[MAX];
    long[] index1=new long[MAX];
    long[] index2=new long[MAX]; 
    long[] index3=new long[MAX];
    long[] index4=new long[MAX]; 

    // storing fibonacci numbers 
    arr[0] = 0; 
    arr[1] = 1; 
    for (int i = 2; i < MAX; i++) 
        arr[i] = arr[i - 1] + arr[i - 2]; 

    // c1 keeps track of number of index of number 
    // divisible by 2 and others c2, c3 and c4 for 
    // 3, 5 and 8 
    int c1 = 0, c2 = 0, c3 = 0, c4 = 0; 

    // separating fibonacci number into their 
    // respective array 
    for (int i = 0; i < MAX; i++) 
    { 
        if (arr[i] % 2 == 0) 
            index1[c1++] = i; 
        if (arr[i] % 3 == 0) 
            index2[c2++] = i; 
        if (arr[i] % 5 == 0) 
            index3[c3++] = i; 
        if (arr[i] % 8 == 0) 
            index4[c4++] = i; 
    } 

    // printing index arrays 
    System.out.print("Index of Fibonacci numbers divisible by" +
        " 2 are :\n"); 
    for (int i = 0; i < c1; i++) 
        System.out.print(index1[i] + " "); 
    System.out.print("\n"); 

    System.out.print("Index of Fibonacci number divisible by" +
        " 3 are :\n"); 
    for (int i = 0; i < c2; i++) 
        System.out.print(index2[i] + " "); 
    System.out.print("\n"); 

    System.out.print("Index of Fibonacci number divisible by" + 
        " 5 are :\n"); 
    for (int i = 0; i < c3; i++) 
        System.out.print(index3[i] + " "); 
    System.out.print("\n"); 

    System.out.print("Index of Fibonacci number divisible by" +
        " 8 are :\n"); 
    for (int i = 0; i < c4; i++) 
        System.out.print(index4[i] + " "); 
    System.out.print("\n"); 
} 
}

// This code is contributed by mits

# Python3 program to demonstrate divisibility
# of Fibonacci numbers. 
MAX = 90; 

# indexes variable stores index of number 
# that is divisible by 2, 3, 5 and 8 
arr = [0] * (MAX);
index1 = [0] * (MAX);
index2 = [0] * (MAX); 
index3 = [0] * (MAX);
index4 = [0] * (MAX); 

# storing fibonacci numbers 
arr[0] = 0; 
arr[1] = 1; 
for i in range(2, MAX): 
    arr[i] = arr[i - 1] + arr[i - 2]; 

# c1 keeps track of number of index 
# of number divisible by 2 and others  
# c2, c3 and c4 for 3, 5 and 8 
c1, c2, c3, c4 = 0, 0, 0, 0;

# separating fibonacci number into
# their respective array 
for i in range(MAX): 
    if (arr[i] % 2 == 0): 
        index1[c1] = i;
        c1 += 1;
    if (arr[i] % 3 == 0): 
        index2[c2] = i;
        c2 += 1;
    if (arr[i] % 5 == 0): 
        index3[c3] = i;
        c3 += 1;
    if (arr[i] % 8 == 0): 
        index4[c4] = i;
        c4 += 1;

# printing index arrays 
print("Index of Fibonacci numbers",
           "divisible by 2 are :"); 
for i in range(c1): 
    print(index1[i], end = " "); 
print(""); 

print("Index of Fibonacci number", 
          "divisible by 3 are :"); 
for i in range(c2): 
    print(index2[i], end = " "); 
print(""); 

print("Index of Fibonacci number", 
          "divisible by 5 are :"); 
for i in range(c3): 
    print(index3[i], end = " "); 
print(""); 

print("Index of Fibonacci number", 
          "divisible by 8 are :"); 
for i in range(c4): 
    print(index4[i], end = " "); 
print("");

# This code is contributed by mits

// C# program to demonstrate divisibility 
// of Fibonacci numbers. 

class GFG{
static int MAX = 90; 

static void Main() 
{ 
    // indexes variable stores index of number that 
    // is divisible by 2, 3, 5 and 8 
    long[] arr = new long[MAX];
    long[] index1 = new long[MAX];
    long[] index2 = new long[MAX]; 
    long[] index3 = new long[MAX];
    long[] index4 = new long[MAX]; 

    // storing fibonacci numbers 
    arr[0] = 0; 
    arr[1] = 1; 
    for (int i = 2; i < MAX; i++) 
        arr[i] = arr[i-1] + arr[i-2]; 

    // c1 keeps track of number of index of number 
    // divisible by 2 and others c2, c3 and c4 for 
    // 3, 5 and 8 
    int c1 = 0, c2 = 0, c3 = 0, c4 = 0; 

    // separating fibonacci number into their 
    // respective array 
    for (int i = 0; i < MAX; i++) 
    { 
        if (arr[i] % 2 == 0) 
            index1[c1++] = i; 
        if (arr[i] % 3 == 0) 
            index2[c2++] = i; 
        if (arr[i] % 5 == 0) 
            index3[c3++] = i; 
        if (arr[i] % 8 == 0) 
            index4[c4++] = i; 
    } 

    // printing index arrays 
    System.Console.Write("Index of Fibonacci numbers" + 
                    "divisible by 2 are :\n"); 
    for (int i = 0; i < c1; i++) 
        System.Console.Write(index1[i]+" "); 
    System.Console.Write("\n"); 

    System.Console.Write("Index of Fibonacci number "+
                        " divisible by 3 are :\n"); 
    for (int i = 0; i < c2; i++) 
        System.Console.Write(index2[i]+" "); 
    System.Console.Write("\n"); 

    System.Console.Write("Index of Fibonacci number "+
        "divisible by 5 are :\n"); 
    for (int i = 0; i < c3; i++) 
        System.Console.Write(index3[i]+" "); 
    System.Console.Write("\n"); 

    System.Console.Write("Index of Fibonacci number "+
        "divisible by 8 are :\n"); 
    for (int i = 0; i < c4; i++) 
        System.Console.Write(index4[i]+" "); 
    System.Console.Write("\n"); 
} 
}

// This code is contributed by mits

// JavaScript program to demonstrate divisibility of Fibonacci 
// numbers. 

var MAX=90; 

// Driver code

    // indexes variable stores index of number that 
    // is divisible by 2, 3, 5 and 8 
    var arr=new Array(MAX);
    var index1= new Array(MAX);
    var index2= new Array(MAX); 
    var index3= new Array(MAX);
    var index4= new Array(MAX); 

    // storing fibonacci numbers 
    arr[0] = 0; 
    arr[1] = 1; 
    for (var i = 2; i < MAX; i++) 
        arr[i] = arr[i - 1] + arr[i - 2]; 

    // c1 keeps track of number of index of number 
    // divisible by 2 and others c2, c3 and c4 for 
    // 3, 5 and 8 
    var c1 = 0, c2 = 0, c3 = 0, c4 = 0; 

    // separating fibonacci number into their 
    // respective array 
    for (var i = 0; i < MAX; i++) 
    { 
        if (arr[i] % 2 == 0) 
            index1[c1++] = i; 
        if (arr[i] % 3 == 0) 
            index2[c2++] = i; 
        if (arr[i] % 5 == 0) 
            index3[c3++] = i; 
        if (arr[i] % 8 == 0) 
            index4[c4++] = i; 
    } 

    // printing index arrays 
    document.write("Index of Fibonacci numbers divisible by" +
        " 2 are :\n"); 
    for (var i = 0; i < c1; i++) 
        document.write(index1[i] + " "); 
    document.write("\n"); 

    document.write("Index of Fibonacci number divisible by" +
        " 3 are :\n"); 
    for (var i = 0; i < c2; i++) 
        document.write(index2[i] + " "); 
    document.write("\n"); 

    document.write("Index of Fibonacci number divisible by" + 
        " 5 are :\n"); 
    for (var i = 0; i < c3; i++) 
        document.write(index3[i] + " "); 
    document.write("\n"); 

    document.write("Index of Fibonacci number divisible by" +
        " 8 are :\n"); 
    for (var i = 0; i < c4; i++) 
        document.write(index4[i] + " "); 
    document.write("\n"); 



// This code is contributed by shivanisinghss2110

<?php
// PHP program to demonstrate divisibility 
// of Fibonacci numbers. 
$MAX = 90; 

// indexes variable stores index of number 
// that is divisible by 2, 3, 5 and 8 
$arr = array($MAX);
$index1 = array($MAX);
$index2 = array($MAX); 
$index3 = array($MAX);
$index4 = array($MAX); 

// storing fibonacci numbers 
$arr[0] = 0; 
$arr[1] = 1; 
for ($i = 2; $i < $MAX; $i++)
{ 
    $arr[$i] = $arr[$i - 1] + $arr[$i - 2];
} 

// c1 keeps track of number of index of 
// number divisible by 2 and others 
// c2, c3 and c4 for 3, 5 and 8 
$c1 = 0;
$c2 = 0;
$c3 = 0;
$c4 = 0; 

// separating fibonacci number into 
// their respective array 
for ($i = 0; $i < $MAX; $i++) 
{ 
    if ($arr[$i] % 2 == 0) 
        $index1[$c1++] = $i; 
    if ($arr[$i] % 3 == 0) 
        $index2[$c2++] = $i; 
    if ($arr[$i] % 5 == 0) 
        $index3[$c3++] = $i; 
    if ($arr[$i] % 8 == 0) 
        $index4[$c4++] = $i; 
} 

// printing index arrays 
echo "Index of Fibonacci numbers divisible by" .
                                " 2 are :\n"; 
for ($i = 0; $i < $c1; $i++) 
    echo $index1[$i] . " "; 
echo "\n"; 

echo "Index of Fibonacci number divisible by" .
                                " 3 are :\n"; 
for ($i = 0; $i < $c2; $i++) 
    echo $index2[$i] . " "; 
echo "\n"; 

echo "Index of Fibonacci number divisible by" .
    " 5 are :\n"; 
for ($i = 0; $i < $c3; $i++) 
    echo $index3[$i] . " "; 
echo "\n"; 

echo "Index of Fibonacci number divisible by" .
    " 8 are :\n"; 
for ($i = 0; $i < $c4; $i++) 
    echo $index4[$i] . " "; 
echo "\n"; 

// This code is contributed by mits
?>

Output: 

Index of Fibonacci numbers divisible by 2 are :
0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 
48 51 54 57 60 63 66 69 72 75 78 81 84 87 
Index of Fibonacci number divisible by 3 are :
0 4 8 12 16 20 24 28 32 36 40 44 48 52 
56 60 64 68 72 76 80 84 88 
Index of Fibonacci number divisible by 5 are :
0 5 10 15 20 25 30 35 40 45 50 
55 60 65 70 75 80 85 
Index of Fibonacci number divisible by 8 are :
0 6 12 18 24 30 36 42 48
54 60 66 72 78 84 

Time Complexity:
The program uses a single for loop of size MAX, to calculate and store the Fibonacci numbers in the array. Hence, the time complexity for this part of the program is O(MAX). The program then uses another for loop of size MAX, to check each number in the array for divisibility by 2, 3, 5, and 8. The time complexity for this part of the program is also O(MAX). Therefore, the overall time complexity of the program is O(MAX).

Space Complexity:
The program uses an array of size MAX to store the Fibonacci numbers. It also uses four separate arrays of sizes c1, c2, c3, and c4, to store the indexes of the Fibonacci numbers that are divisible by 2, 3, 5, and 8 respectively. The maximum size of these arrays is equal to MAX/3 (when all Fibonacci numbers are divisible by 2). Therefore, the space complexity of the program is O(MAX).
3. Fibonacci number with index number factor : We have some Fibonacci number like F(1) = 1 which is divisible by 1, F(5) = 5 which is divisible by 5, F(12) = 144 which is divisible by 12, F(24) = 46368 which is divisible by 24, F(25) = 75025 which is divisible by 25. This type of index number follow a certain pattern. First, let's keep a look on those index number : 
1, 5, 12, 24, 25, 36, 48, 60, 72, 84, 96, 108, 120, 125, 132, ..... 

On observing it, this series is made up of every number that is multiple of 12 as well as all the number that satisfies the condition of pow(5, k), where k = 0, 1, 2, 3, 4, 5, 6, 7, .......

// C++ program to demonstrate that Fibonacci numbers
// that are divisible by their indexes have indexes
// as either power of 5 or multiple of 12.
#include<iostream>
using namespace std;
#define MAX 100

int main()
{
  
    // storing Fibonacci numbers
    long long int arr[MAX];
    arr[0] = 0;
    arr[1] = 1;
    for (int i = 2; i < MAX; i++)
        arr[i] = arr[i-1] + arr[i-2];

    cout<<"Fibonacci numbers divisible by "
          "their indexes are :\n";
    for (int i = 1; i < MAX; i++)
        if (arr[i] % i == 0)
            cout<<"  "<< i;
}

// This code is contributed by shivanisinghss2110

// C program to demonstrate that Fibonacci numbers
// that are divisible by their indexes have indexes
// as either power of 5 or multiple of 12.
#include<stdio.h>
#define MAX 100

int main()
{
    // storing Fibonacci numbers
    long long int arr[MAX];
    arr[0] = 0;
    arr[1] = 1;
    for (int i = 2; i < MAX; i++)
        arr[i] = arr[i-1] + arr[i-2];

    printf("Fibonacci numbers divisible by "
          "their indexes are :\n");
    for (int i = 1; i < MAX; i++)
        if (arr[i] % i == 0)
            printf("%d  ", i);
}

// Java program to demonstrate that Fibonacci numbers 
// that are divisible by their indexes have indexes 
// as either power of 5 or multiple of 12. 

class GFG
{

static int MAX = 100; 

public static void main(String[] args) 
{ 
    // storing Fibonacci numbers 
    long[] arr = new long[MAX]; 
    arr[0] = 0; 
    arr[1] = 1; 
    for (int i = 2; i < MAX; i++) 
        arr[i] = arr[i - 1] + arr[i - 2]; 

    System.out.print("Fibonacci numbers divisible by "+
        "their indexes are :\n"); 
    for (int i = 1; i < MAX; i++) 
        if (arr[i] % i == 0) 
            System.out.print(i + " "); 
}
}

// This code is contributed by mits

# Python3 program to demonstrate that Fibonacci numbers
# that are divisible by their indexes have indexes
# as either power of 5 or multiple of 12.

if __name__=='__main__':
    MAX = 100
# storing Fibonacci numbers
    arr = [0 for i in range(MAX)]
    arr[0] = 0
    arr[1] = 1
    for i in range(2, MAX):
        arr[i] = arr[i - 1] + arr[i - 2]

    print("Fibonacci numbers divisible by their indexes are :")
    for i in range(1, MAX):
        if(arr[i] % i == 0):
            print(i,end=" ")

# This code is contributed by
# Sanjit_Prasad

// C# program to demonstrate that Fibonacci 
// numbers that are divisible by their 
// indexes have indexes as either power of 5 
// or multiple of 12. 
using System;

class GFG
{
static int MAX = 100; 
static void Main() 
{ 
    // storing Fibonacci numbers 
    long[] arr = new long[MAX]; 
    arr[0] = 0; 
    arr[1] = 1; 
    for (int i = 2; i < MAX; i++) 
        arr[i] = arr[i - 1] + arr[i - 2]; 

    Console.Write("Fibonacci numbers divisible by " +
                           "their indexes are :\n"); 
    for (int i = 1; i < MAX; i++) 
        if (arr[i] % i == 0) 
            System.Console.Write(i+" "); 
}
}

// This code is contributed by mits

// JavaScript program to demonstrate that Fibonacci numbers 
// that are divisible by their indexes have indexes 
// as either power of 5 or multiple of 12. 

var MAX = 100; 
 
    // storing Fibonacci numbers 
    var arr = new Array(MAX); 
    arr[0] = 0; 
    arr[1] = 1; 
    for (var i = 2; i < MAX; i++) 
        arr[i] = arr[i - 1] + arr[i - 2]; 

    document.write("Fibonacci numbers divisible by their indexes are :"); 
    for (var i = 1; i < MAX; i++) 
        if (arr[i] % i == 0) 
            document.write(i + " "); 


// This code is contributed by shivanisinghss2110

Output: 

Fibonacci numbers divisible by their indexes are :
1  5  12  24  25  36  48  60  72  96

4. Value of f(n-1)*f(n+1) - f(n)*f(n) is (-1)ⁿ. Please refer Cassini’s Identity for details.

5. The sum of any ten consecutive Fibonacci numbers is divisible by 11.

    Example: 0+1+1+ 2+3+ 5+ 8+13+21+34 =88 which is divisible by 11.

    Proof: Just write every term in the sum in terms of F1 and F2, keeping in mind that Fn = Fn-1 + Fn-2.
    F1+F2+(F1+F2)+(F1+2F2)+(2F1+3F2)+(3F1+5F2)+(5F1+8F2)+(8F1+13F2)+(13F1+21F2)+(21F1+34F2). 

Then the sum is clearly equal to 55F1+88F2=11(5F1+8F2), which is divisible by 11.
 

Reference : 
https://r-knott.surrey.ac.uk/Fibonacci/fibmaths.html