a(n) = (7*n^2 + 7*n - 12)/2.

Terms

a(0) =1a(1) =15a(2) =36a(3) =64a(4) =99a(5) =141a(6) =190a(7) =246a(8) =309a(9) =379a(10) =456a(11) =540a(12) =631a(13) =729a(14) =834a(15) =946a(16) =1065a(17) =1191a(18) =1324a(19) =1464a(20) =1611a(21) =1765a(22) =1926a(23) =2094a(24) =2269a(25) =2451a(26) =2640a(27) =2836a(28) =3039a(29) =3249