a(n) = (n^3 + 5*n + 18)/6.

Terms

a(0) =0a(1) =2a(2) =3a(3) =4a(4) =6a(5) =10a(6) =17a(7) =28a(8) =44a(9) =66a(10) =95a(11) =132a(12) =178a(13) =234a(14) =301a(15) =380a(16) =472a(17) =578a(18) =699a(19) =836a(20) =990a(21) =1162a(22) =1353a(23) =1564a(24) =1796a(25) =2050a(26) =2327a(27) =2628a(28) =2954a(29) =3306