Problem 135
Same differences

Given the positive integers, x, y, and z, are consecutive terms of an arithmetic progression, the least value of the positive integer, n, for which the equation, x2−y2−z2 = n, has exactly two solutions is n = 27:

342− 272− 202 = 122− 92− 62 = 27

It turns out that n = 1155 is the least value which has exactly ten solutions.

How many values of n less than one million have exactly ten distinct solutions?

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http://projecteuler.net/problem=135