61999domain: NAppears in sequencesNonnegative values x of solutions (x, y) to the Diophantine equation x^2+(x+521)^2 = y^2.at n=9A129725Numbers k such that k!*2^k + 1 is prime.at n=6A256594a(n) is the least number k such that the sum of n^2 consecutive primes starting at prime(k) is a square.at n=27A357813