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Python program to count number of trailing zeros in Factorial of number N
Learn how to count number of trailing zeros in factorial of N using Python program.
By Ankit Rai Last updated : January 04, 2024
Problem statement
Given a number, write a Python program to count number of trailing zeros in factorial of N.
Formula used
Trailing 0s in N! = Count of 5s in prime factors of n!
= floor(n/5) + floor(n/25) + floor(n/125) + ....
Example
Input: N = 23
Output: 4
Factorial of 23 is 25852016738884976640000 which has four trailing 0.
Input: N = 25
Output: 6
Factorial of 25 is 15511210043330985984000000 which has six trailing 0.
Python program to count number of trailing zeros in Factorial of number N
# Define a function for finding
# number of trailing zeros in N!
def find_trailing_zeros(num):
sum = 0
i = 1
# iterating untill quotient is not zero
while True:
# take integer divison
quotient = num // (5**i)
if quotient == 0:
break
sum += quotient
i += 1
return sum
# Driver code
if __name__ == "__main__":
# assigning a number
num = 10
# function call
print(
"Number of trailing zeros in factorial of",
num,
"is :",
find_trailing_zeros(num),
)
num = 20
print(
"Number of trailing zeros in factorial of",
num,
"is :",
find_trailing_zeros(num),
)
Output
The output of the above example is:
Number of trailing zeros in factorial of 10 is : 2
Number of trailing zeros in factorial of 20 is : 4
Python Basic Programs »
To understand the above program, you should have the basic knowledge of the following Python topics: