This question takes me back to 2004!

How many positive integer divisors of 200 4 2004 2004^{2004} are divisible by exactly 2004 2004 positive integers?


This question is from 2004 AIME II.


The answer is 54.

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1 solution

Parth Lohomi
Dec 18, 2014

The prime factorization of 2004 is 2 2 3 167 2^2\cdot 3\cdot 167 . Thus the prime factorization of 200 4 2004 2004^{2004} is 2 4008 3 2004 16 7 2004 2^{4008}\cdot 3^{2004}\cdot 167^{2004} . We can count the number of divisors of a number by multiplying together one more than each of the exponents of the prime factors in its prime factorization. For example, the number of divisors of 2004 = 2 2 3 1 16 7 1 i s ( 2 + 1 ) ( 1 + 1 ) ( 1 + 1 ) = 12 2004=2^2\cdot 3^1\cdot 167^1 is (2+1)(1+1)(1+1)=12 A positive integer divisor of 200 4 2004 2004^{2004} will be of the form 2 a 3 b 16 7 c 2^a\cdot 3^b\cdot 167^c Thus we need to find how many (a,b,c) satisfy ( a + 1 ) ( b + 1 ) ( c + 1 ) = 2 2 3 167 (a+1)(b+1)(c+1)=2^2\cdot 3\cdot 167 We can think of this as partitioning the exponents to a+1, b+1, and c+1. So let's partition the 2's first. There are two 2's so this is equivalent to partitioning two items in three containers. We can do this in ( 4 2 ) {4 \choose 2} = 6 ways. We can partition the 3 in three ways and likewise we can partition the 167 in three ways. So we have 6 3 3 = 54 6\cdot 3\cdot 3 = 54 as our answer.

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Parth Lohomi - 6 years, 5 months ago

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Copied from AoPS...... Dont worry....... I also saw the solution on the website.....

Mehul Arora - 6 years, 4 months ago

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