a(n) = (n^3 + 6*n^2 + 17*n + 6)/6.

Terms

a(0) =1a(1) =5a(2) =12a(3) =23a(4) =39a(5) =61a(6) =90a(7) =127a(8) =173a(9) =229a(10) =296a(11) =375a(12) =467a(13) =573a(14) =694a(15) =831a(16) =985a(17) =1157a(18) =1348a(19) =1559a(20) =1791a(21) =2045a(22) =2322a(23) =2623a(24) =2949a(25) =3301a(26) =3680a(27) =4087a(28) =4523a(29) =4989