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

Terms

a(0) =1a(1) =25a(2) =121a(3) =289a(4) =529a(5) =841a(6) =1225a(7) =1681a(8) =2209a(9) =2809a(10) =3481a(11) =4225a(12) =5041a(13) =5929a(14) =6889a(15) =7921a(16) =9025a(17) =10201a(18) =11449a(19) =12769a(20) =14161a(21) =15625a(22) =17161a(23) =18769a(24) =20449a(25) =22201a(26) =24025a(27) =25921a(28) =27889a(29) =29929