Problem 44071. Smallest n, for n! to have m trailing zero digits

Created by Jihye Sofia Seo in Community

For given positive integer n, its factorial often has many trailing zeros, in other words many factors of 10s. In order for n! to have at least "m" trailing zeros, what is the smallest "n" ?

Example: factorial(10) = 3628800 factorial(9) = 362880 In order to have 2 trailing zeros on factorial, the smallest n is 10.

Optional: Can you make an efficient algorithm for a very large m?

Solution Stats

77.5% Correct | 22.5% Incorrect
Last solution submitted on Feb 10, 2019

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