a(n) = (2*n^3 + 5*n^2 - 7*n)/2.

Terms

a(0) =0a(1) =11a(2) =39a(3) =90a(4) =170a(5) =285a(6) =441a(7) =644a(8) =900a(9) =1215a(10) =1595a(11) =2046a(12) =2574a(13) =3185a(14) =3885a(15) =4680a(16) =5576a(17) =6579a(18) =7695a(19) =8930a(20) =10290a(21) =11781a(22) =13409a(23) =15180a(24) =17100a(25) =19175a(26) =21411a(27) =23814a(28) =26390a(29) =29145