Maths Olympiad Prep

Library / /12 of 377

Number theory Difficulty 4.1 AIME Find the answer United States

Problem:

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

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

Solution

Solution:

Answer: 9. 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.

Want a route through all this instead of an archive? The track puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.

Source: MathNet, licensed CC-BY-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.