a(n) = n*(2*n^2 + 5*n + 15)/2.

Terms

a(0) =0a(1) =11a(2) =33a(3) =72a(4) =134a(5) =225a(6) =351a(7) =518a(8) =732a(9) =999a(10) =1325a(11) =1716a(12) =2178a(13) =2717a(14) =3339a(15) =4050a(16) =4856a(17) =5763a(18) =6777a(19) =7904a(20) =9150a(21) =10521a(22) =12023a(23) =13662a(24) =15444a(25) =17375a(26) =19461a(27) =21708a(28) =24122a(29) =26709