a(n) = (1/2)*(n^3 - 6*n^2 + 13*n - 6).

Terms

a(0) =1a(1) =2a(2) =3a(3) =7a(4) =17a(5) =36a(6) =67a(7) =113a(8) =177a(9) =262a(10) =371a(11) =507a(12) =673a(13) =872a(14) =1107a(15) =1381a(16) =1697a(17) =2058a(18) =2467a(19) =2927a(20) =3441a(21) =4012a(22) =4643a(23) =5337a(24) =6097a(25) =6926a(26) =7827a(27) =8803a(28) =9857a(29) =10992