Perfect before 2016 ends

Find the number of perfect squares less than or equal to 2016 that can be expressed as a 4 + 5 b c ( a 2 + b ) + 2 a^4 + 5bc(a^2 + b) + 2 for some nonnegative integers a a , b b , and c c .

This problem is part of the set " Symphony "


The answer is 0.

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1 solution

Rindell Mabunga
Dec 16, 2016

Working in modulo 5 5 ,

Perfect squares can only be 0 ( m o d 5 ) 0(mod 5) or ± 1 ( m o d 5 ) \pm 1(mod 5)

a 4 0 , 1 ( m o d 5 ) a^4 \equiv 0, 1 (mod 5)

5 b c ( a 2 + b ) 0 ( m o d 5 ) 5bc(a^2 + b) \equiv 0(mod 5)

2 2 ( m o d 5 ) 2 \equiv 2(mod 5)

The expression can be either 2 ( m o d 5 ) 2 (mod 5) or 3 ( m o d 5 ) 3 (mod 5) but as I said earlier there are no perfect squares that are either 2 ( m o d 5 ) 2(mod 5) or 3 ( m o d 5 ) 3(mod 5)

Therefore, there are no possible perfect square that would satisfy the expression.

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