3266629domain: NAppears in sequencesPositive numbers y such that y^2 is of the form x^2 + (x + 569)^2 with integer x.at n=16A160090G.f.: Sum_{n>=0} x^n / (1-2*x)^(2*n+1) * [Sum_{k=0..n} C(n,k)^2 * 2^k * x^k] * [Sum_{k=0..n} C(n,k)^2 * 4^k * x^k].at n=8A249921