a(n) = 4*(n+1)*n + 5.

Terms

a(0) =5a(1) =13a(2) =29a(3) =53a(4) =85a(5) =125a(6) =173a(7) =229a(8) =293a(9) =365a(10) =445a(11) =533a(12) =629a(13) =733a(14) =845a(15) =965a(16) =1093a(17) =1229a(18) =1373a(19) =1525a(20) =1685a(21) =1853a(22) =2029a(23) =2213a(24) =2405a(25) =2605a(26) =2813a(27) =3029a(28) =3253a(29) =3485