a(n) = (12*n + 3)^2.

Terms

a(0) =9a(1) =225a(2) =729a(3) =1521a(4) =2601a(5) =3969a(6) =5625a(7) =7569a(8) =9801a(9) =12321a(10) =15129a(11) =18225a(12) =21609a(13) =25281a(14) =29241a(15) =33489a(16) =38025a(17) =42849a(18) =47961a(19) =53361a(20) =59049a(21) =65025a(22) =71289a(23) =77841a(24) =84681a(25) =91809a(26) =99225a(27) =106929a(28) =114921a(29) =123201