What is a Strong Number?
A Strong number is one that is equal to the sum of the factorial of its digits.
Example
145 Factorial of 1=1 Factorial of 4=24 Factorial of 5=120 Sum=1+24+120 =145
Following program is to find if the input number is a strong number or not. Return ‘True’ if the number is a strong number, else return ‘False’.
We are using two functions isStrong() which determines whether the number is strong or not, second method is factorial() which returns the factorial of the passed digit.
The factorial() is called from inside isStrong() to get factorials of all the digits(n%10) and add it to the sum.
After factorial of all the digits are summed up, the sum is compared to the original number, if they are equal, true is returned, else false is returned.
Why are we copying n into num in isStrong() ? On iterating through the while loop, the value of n will change to zero.But we require the original value to be compared with the sum later on and hence, we need to copy value of n into some variable before it is changed.
The factorial() uses recursion to calculate the factorial of the digits.
Example
def factorial(d):
if(d==1 or d==0):
return 1
return d*factorial(d-1)
def isStrong(n):
num=n
sm=0
while(n>0):
digit=n%10
sm=sm+factorial(digit)
n=n//10
if(sm==num):
return True
else:
return False
print("Input a number")
a=int(input())
print(isStrong(a))Output
Input a number 145 True