a(n) = (8*n^3 + 15*n^2 + 13*n)/6.

Terms

a(0) =0a(1) =6a(2) =25a(3) =65a(4) =134a(5) =240a(6) =391a(7) =595a(8) =860a(9) =1194a(10) =1605a(11) =2101a(12) =2690a(13) =3380a(14) =4179a(15) =5095a(16) =6136a(17) =7310a(18) =8625a(19) =10089a(20) =11710a(21) =13496a(22) =15455a(23) =17595a(24) =19924a(25) =22450a(26) =25181a(27) =28125a(28) =31290a(29) =34684