244650domain: NAppears in sequencesa(1) = 1, a(n+1)= smallest triangular number greater than the n-th partial sum.at n=17A076971Triangular numbers T from A000217 such that (4*T+1)/13 is prime.at n=32A208294Multiplicative orders of 2+-i modulo p == 3 (mod 4) that are congruent to 2 modulo 4.at n=10A385218