a(n) = 6*n^2 - 1.

Terms

a(0) =-1a(1) =5a(2) =23a(3) =53a(4) =95a(5) =149a(6) =215a(7) =293a(8) =383a(9) =485a(10) =599a(11) =725a(12) =863a(13) =1013a(14) =1175a(15) =1349a(16) =1535a(17) =1733a(18) =1943a(19) =2165a(20) =2399a(21) =2645a(22) =2903a(23) =3173a(24) =3455a(25) =3749a(26) =4055a(27) =4373a(28) =4703a(29) =5045