13082624domain: NAppears in sequencesa(0) = 1, a(1) = 3; for n > 1, a(n) = 2*a(n-1) + 4*a(n-2).at n=14A063782Smallest number k that cannot be expressed as x^2 + y^2 + z^2 + w^2 where x >= y >= z >= w >= 0 and x > floor(sqrt(k)) - n, but can be so expressed if x = floor(sqrt(k)) - n.at n=31A285552