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Lattice Points on a Circle

 Published on Friday, 20th February 2009, 09:00 pm; Solved by 2657;
Difficulty: Level 33 [85%]

Problem 233

Let $f(N)$ be the number of points with integer coordinates that are on a circle passing through $(0,0)$, $(N,0)$,$(0,N)$, and $(N,N)$.

It can be shown that $f(10000) = 36$.

What is the sum of all positive integers $N \le 10^{11}$ such that $f(N) = 420$?



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