# Write a Python program to find if a number is strong number or not

PythonServer Side ProgrammingProgramming

## 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