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

Terms

a(0) =-1a(1) =1a(2) =7a(3) =17a(4) =31a(5) =49a(6) =71a(7) =97a(8) =127a(9) =161a(10) =199a(11) =241a(12) =287a(13) =337a(14) =391a(15) =449a(16) =511a(17) =577a(18) =647a(19) =721a(20) =799a(21) =881a(22) =967a(23) =1057a(24) =1151a(25) =1249a(26) =1351a(27) =1457a(28) =1567a(29) =1681