a(n) = (2*n^3 + 5*n^2 - 9*n)/2.

Terms

a(0) =-1a(1) =9a(2) =36a(3) =86a(4) =165a(5) =279a(6) =434a(7) =636a(8) =891a(9) =1205a(10) =1584a(11) =2034a(12) =2561a(13) =3171a(14) =3870a(15) =4664a(16) =5559a(17) =6561a(18) =7676a(19) =8910a(20) =10269a(21) =11759a(22) =13386a(23) =15156a(24) =17075a(25) =19149a(26) =21384a(27) =23786a(28) =26361a(29) =29115