Number Theory problem 1 by Dhaval Furia

How many factors of 2 4 3 5 1 0 4 2^{4} 3^{5} 10^{4} are perfect squares which are greater than 1 1 ?


The answer is 44.

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2 solutions

2 4 3 5 1 0 4 = ( 4 4 9 2 2 5 2 ) 3 2^43^510^4=(4^49^225^2)3 . So, in all, there are ( 4 + 1 ) ( 2 + 1 ) ( 2 + 1 ) (4+1)(2+1)(2+1) or 45 45 such square factors, of which the number of such factors greater than 1 1 is 44 \boxed {44} .

Dhaval Furia
May 14, 2020

Prime factorization of 2^4 x 3^5 x 10^4 is 2^8 x 3^5 x 5^4

So in the prime factorization of a perfect square factor of this number, the power of 2 can be anything from 0, 2, 4, 6, 8 (5 choices)

Similarly, that of 3 can be anything from 0, 2, 4 (3 choices)

And that of 5 can be anything from 0, 2, 4 (3 choices)

Hence, (by Multiplication Counting Principle), there are 5x3x3 = 45 possible perfect square factors

But this also includes 1 (when powers of 2, 3 and 5 are all 0)

Since we want the count of perfect squares greater than 1, it will be 45 - 1 = 44

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