a(n) = n*(n^3 - n + 2)/2.

Terms

a(0) =0a(1) =1a(2) =8a(3) =39a(4) =124a(5) =305a(6) =636a(7) =1183a(8) =2024a(9) =3249a(10) =4960a(11) =7271a(12) =10308a(13) =14209a(14) =19124a(15) =25215a(16) =32656a(17) =41633a(18) =52344a(19) =64999a(20) =79820a(21) =97041a(22) =116908a(23) =139679a(24) =165624a(25) =195025a(26) =228176a(27) =265383a(28) =306964a(29) =353249