a(n) = 8*n^2 - 4*n - 3.

Terms

a(0) =1a(1) =21a(2) =57a(3) =109a(4) =177a(5) =261a(6) =361a(7) =477a(8) =609a(9) =757a(10) =921a(11) =1101a(12) =1297a(13) =1509a(14) =1737a(15) =1981a(16) =2241a(17) =2517a(18) =2809a(19) =3117a(20) =3441a(21) =3781a(22) =4137a(23) =4509a(24) =4897a(25) =5301a(26) =5721a(27) =6157a(28) =6609a(29) =7077