I'm so excited, I used a factorial!

Find the number of trailing zeros in the base-17 representation of 2017 ! . 2017!.

Clarification : 2017, as it is written here, is in base 10.


The answer is 124.

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1 solution

Andy Hayes
Nov 9, 2016

The power of 17 in 2017 ! 2017! is:

v 17 ( 2017 ) = 2017 17 + 2017 1 7 2 = 118 + 6 = 124 \begin{aligned} v_{17}(2017) &= \left\lfloor \frac{2017}{17} \right\rfloor + \left\lfloor \frac{2017}{17^2} \right\rfloor \\ &= 118 + 6 \\ &= 124 \end{aligned}

2017 ! = 1 7 124 × k , 2017!=17^{124} \times k, where k k is an integer such that 17 k . 17 \nmid k.

Therefore, there are 124 \boxed{124} trailing zeros in the base-17 representation of 2017 ! 2017! .

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