1414561domain: NAppears in sequencesNumbers k such that sigma((k + 1) / 2) is a prime q.at n=34A292446Centered octachoral numbers.at n=20A365206a(n) = Sum_{1 <= x_1, x_2, x_3, x_4 <= n} gcd(x_1, x_2, x_3, x_4, n)^4.at n=28A372931