Let P n be the product of all positive divisors of a positive integer n . For example, P 1 = 1 and P 4 = 1 × 2 × 4 = 8 .
If 2 m is the highest integer power of 2 that divides P 3 6 0 0 0 , what is m ?
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Yes, that is the one!
Here is a Mathematica code that outputs the Prime factors of this product
FactorInteger[Times @@ Divisors@36000]
which returns
{{2, 180}, {3, 72}, {5, 108}}
so, the answer is 180
Which computer language is this?
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Mathematica ...
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Oops, sorry. I have not heard it before.
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@Ong Zi Qian
–
you can test Mathematica online here https://sandbox.open.wolframcloud.com
Just paste the code and hit shift+enter to run
Also under the "Help" tab you will find the documentation which is an excellent guide to the features of this language
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@Giorgos K. – Oh, I got it. Thank you!
@Giorgos K. – But why do I cannot toggle your LaTeX?
First of all note that, 3 6 0 0 0 = 2 5 × 3 2 × 5 3 . As we know that from number theory,
the product of positive divisors of n ∈ N = n 2 τ ( n ) where τ ( n ) = number of positive divisors of n ∈ N .
τ ( 3 6 0 0 0 ) = τ ( 2 5 × 3 2 × 5 3 ) = ( 5 + 1 ) × ( 2 + 1 ) × ( 3 + 1 ) = 7 2
This imply,
P 3 6 0 0 0 = 3 6 0 0 0 3 6 = ( 2 5 × 3 2 × 5 3 ) 3 6 = ( 2 5 ) 3 6 × ( 3 2 ) 3 6 × ( 5 3 ) 3 6
Which clearly imply the highest integer powers of 2 that divides P 3 6 0 0 0 is ( 2 5 ) 3 6 = 2 1 8 0 this imply m = 1 8 0
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Note that 3 6 0 0 0 = 2 5 ⋅ 3 2 ⋅ 5 3 . Also, note that a divisor of 3 6 0 0 0 is of the form 2 a ⋅ 3 b ⋅ 5 c ( a , b , c ∈ N 0 ) , where a ≤ 5 , b ≤ 2 and c ≤ 3 . Then, for a fixed a , 2 a appears 3 ⋅ 4 = 1 2 times among the divisors of 3 6 0 0 0 .
Knowing that, as a takes values from 0 to 5 , the highest integer power of 2 that divides P 3 6 0 0 0 is i = 0 ∏ 5 ( 2 i ) 1 2 = ( 2 1 + 2 + 3 + 4 + 5 ) 1 2 = 2 1 8 0 .