a(n) = (n^3 + 6n^2 - n + 12)/6.

Terms

a(0) =2a(1) =3a(2) =7a(3) =15a(4) =28a(5) =47a(6) =73a(7) =107a(8) =150a(9) =203a(10) =267a(11) =343a(12) =432a(13) =535a(14) =653a(15) =787a(16) =938a(17) =1107a(18) =1295a(19) =1503a(20) =1732a(21) =1983a(22) =2257a(23) =2555a(24) =2878a(25) =3227a(26) =3603a(27) =4007a(28) =4440a(29) =4903