a(n) = (9n^2 + 9n + 4)/2.

Terms

a(0) =2a(1) =11a(2) =29a(3) =56a(4) =92a(5) =137a(6) =191a(7) =254a(8) =326a(9) =407a(10) =497a(11) =596a(12) =704a(13) =821a(14) =947a(15) =1082a(16) =1226a(17) =1379a(18) =1541a(19) =1712a(20) =1892a(21) =2081a(22) =2279a(23) =2486a(24) =2702a(25) =2927a(26) =3161a(27) =3404a(28) =3656a(29) =3917