Maths Olympiad Prep

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Number theory Difficulty 5.0 AIME Find the answer

Compute the largest positive integer such that 2007!2007n\frac{2007!}{2007^{n}} is an integer.

A number or a short expression. Spacing and $ signs are ignored.

Solution

Note that 2007=322232007=3^{2} \cdot 223. Using the fact that the number of times a prime pp divides n!n! is given by np+np2+np3+\left\lfloor\frac{n}{p}\right\rfloor+\left\lfloor\frac{n}{p^{2}}\right\rfloor+\left\lfloor\frac{n}{p^{3}}\right\rfloor+\cdots it follows that the answer is 9.

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