A strong number is a number, where the sum of the factorial of the digits is equal to the number itself.
Example
- 123!= 1!+2!+3!
=1+2+6 =9
Here, 123 is not a strong number because, the sum of factorial of digits is not equal to the number itself.
- 145!=1!+4!+5!
=1+24+120
=145
Here, 145 is a strong number because, the sum of factorial of digits is equal to the number itself.
The logic we use to find whether the given number is strong or not is as follows −
while(n){
i = 1,fact = 1;
rem = n % 10;
while(i <= rem){
fact = fact * i;
i++;
}
sum = sum + fact;
n = n / 10;
}
if(sum == temp)
printf("%d is a strong number\n",temp);
else
printf("%d is not a strong number\n",temp);Program
Following is the C program to find whether the given number is strong or not −
#include<stdio.h>
int main(){
int n,i;
int fact,rem;
printf("\nEnter a number : ");
scanf("%d",&n);
printf("\n");
int sum = 0;
int temp = n;
while(n){
i = 1,fact = 1;
rem = n % 10;
while(i <= rem){
fact = fact * i;
i++;
}
sum = sum + fact;
n = n / 10;
}
if(sum == temp)
printf("%d is a strong number\n",temp);
else
printf("%d is not a strong number\n",temp);
return 0;
}Output
When the above program is executed, it produces the following result −
Run 1: Enter a number : 145 145 is a strong number Run 2: Enter a number : 25 25 is not a strong number