How many positive integer divisors of are divisible by exactly positive integers?
This question is from 2004 AIME II.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
The prime factorization of 2004 is 2 2 ⋅ 3 ⋅ 1 6 7 . Thus the prime factorization of 2 0 0 4 2 0 0 4 is 2 4 0 0 8 ⋅ 3 2 0 0 4 ⋅ 1 6 7 2 0 0 4 . 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 2 0 0 4 = 2 2 ⋅ 3 1 ⋅ 1 6 7 1 i s ( 2 + 1 ) ( 1 + 1 ) ( 1 + 1 ) = 1 2 A positive integer divisor of 2 0 0 4 2 0 0 4 will be of the form 2 a ⋅ 3 b ⋅ 1 6 7 c Thus we need to find how many (a,b,c) satisfy ( a + 1 ) ( b + 1 ) ( c + 1 ) = 2 2 ⋅ 3 ⋅ 1 6 7 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 ( 2 4 ) = 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 = 5 4 as our answer.