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

## 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*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.**n**into**num**in**isStrong()**?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

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