a(n) = 3*n^3 - 1.

Terms

a(0) =-1a(1) =2a(2) =23a(3) =80a(4) =191a(5) =374a(6) =647a(7) =1028a(8) =1535a(9) =2186a(10) =2999a(11) =3992a(12) =5183a(13) =6590a(14) =8231a(15) =10124a(16) =12287a(17) =14738a(18) =17495a(19) =20576a(20) =23999a(21) =27782a(22) =31943a(23) =36500a(24) =41471a(25) =46874a(26) =52727a(27) =59048a(28) =65855a(29) =73166