a(n) = n*(2*n^2 + 5*n + 17)/2.

Terms

a(0) =0a(1) =12a(2) =35a(3) =75a(4) =138a(5) =230a(6) =357a(7) =525a(8) =740a(9) =1008a(10) =1335a(11) =1727a(12) =2190a(13) =2730a(14) =3353a(15) =4065a(16) =4872a(17) =5780a(18) =6795a(19) =7923a(20) =9170a(21) =10542a(22) =12045a(23) =13685a(24) =15468a(25) =17400a(26) =19487a(27) =21735a(28) =24150a(29) =26738