184760domain: NAppears in sequencesa(n) = Sum_{k=1..n-1} k*sigma(k)*sigma(n-k).at n=30A0004414-dimensional figurate numbers: a(n) = (5*n-1)*binomial(n+2,3)/4.at n=30A002418a(n) = n^4 + 3*n^3 + 2*n^2 - 2*n.at n=20A330651