151633domain: NAppears in sequencesa(n) = Sum_{k=0..n-3} T(n,k) * T(n,k+3), with T given by A026725.at n=7A027210Numbers n such that (n(n+1)/2) modulo sigma(n) = n.at n=19A232538Let q be the n-th prime power (A246655), then a(n) = q^3 + q^2 - q; number of solutions to x*y = z*w in the finite field F_q.at n=23A367014