A divisive year

In how many ways can 2016 be expressed as the product of three integers, where the order of the factors matters?


The answer is 1512.

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1 solution

Siva Bathula
Mar 31, 2016

2016 can be factorized as 2 5 3 2 7 1 2^{5}\ast 3^{2}\ast7^{1} . If we need to arrange this into three factors, ( a 1 , a 2 , a 3 ) (a{_1},a{_2},a{_3}) then we have a 1 a 2 a 3 a{_1}*a{_2}*a{_3} = 2016. So each of a 1 , a 2 , a 3 a{_1}, a{_2}, a{_3} can be expressed as powers of prime factors, a i = 2 x i 3 y i 7 z i a{_i} = 2^{x{_i}} \ast 3^{y{_i}} \ast 7^{z{_i}} . We have three equations i = 1 3 x i = 5 , i = 1 3 y i = 2 , i = 1 3 z i = 1 \sum_{i=1}^3 x{_i} = 5, \sum_{i=1}^3 y{_i} = 2 , \sum_{i=1}^3 z{_i} = 1 . Its easy to see the total number of possibilities are 7 c 2 4 c 2 3 c 2 7c{_2} \ast 4c{_2} \ast 3c{_2} = 378. Since the problem states 'integers', we need to consider the possibilities where 2 among a i a{_i} 's are negative. So that gives us 3 c 2 3c{_2} more possibilities. So total = ( 3 c 2 + 1 ) 378 (3c{_2} + 1) \ast 378 = 1512 \boxed{1512}

Yes, very clearly explained! Thanks! (+1)

Otto Bretscher - 5 years, 2 months ago

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