a(n) = 4*n^2 - 1.

Terms

a(0) =-1a(1) =3a(2) =15a(3) =35a(4) =63a(5) =99a(6) =143a(7) =195a(8) =255a(9) =323a(10) =399a(11) =483a(12) =575a(13) =675a(14) =783a(15) =899a(16) =1023a(17) =1155a(18) =1295a(19) =1443a(20) =1599a(21) =1763a(22) =1935a(23) =2115a(24) =2303a(25) =2499a(26) =2703a(27) =2915a(28) =3135a(29) =3363