Project Euler #136: Singleton difference

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    way to solution

    13^2−10^2−7^2=20 (a+x)^2 - a^2 - (a-x)^2 = n

    a^2+2ax+x^2-a^2-(a^2-2ax+x^2) = n

    a^2+2ax+x^2-a^2-a^2+2ax-x^2 = n 4ax-a^2 = n a(4x-a) = n

    Since n, x and a are integers it raises following conditions,

    n%a==0;

    The interesing thing is that, n should be perfectly divisible by a

    4x-a = n/a 4x = n/a + a