a(n) = n*(n + a(n-1)) with a(0)=0.

Terms

a(0) =0a(1) =1a(2) =6a(3) =27a(4) =124a(5) =645a(6) =3906a(7) =27391a(8) =219192a(9) =1972809a(10) =19728190a(11) =217010211a(12) =2604122676a(13) =33853594957a(14) =473950329594