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

Terms

a(0) =1a(1) =49a(2) =169a(3) =361a(4) =625a(5) =961a(6) =1369a(7) =1849a(8) =2401a(9) =3025a(10) =3721a(11) =4489a(12) =5329a(13) =6241a(14) =7225a(15) =8281a(16) =9409a(17) =10609a(18) =11881a(19) =13225a(20) =14641a(21) =16129a(22) =17689a(23) =19321a(24) =21025a(25) =22801a(26) =24649a(27) =26569a(28) =28561a(29) =30625