912600domain: NAppears in sequencesa(n) = 2*(n+1)*binomial(n+2,4).at n=23A027777Prime power perfect numbers: If n = Product p_i^r_i let PPsigma(n) = Product {Sum p_i^s_i, 2<=s_i<=r_i, s_i is prime}; sequence gives numbers k such that PPsigma(k) = 2*k.at n=19A096290