a(n) = (9*n + 3)^2.

Terms

a(0) =9a(1) =144a(2) =441a(3) =900a(4) =1521a(5) =2304a(6) =3249a(7) =4356a(8) =5625a(9) =7056a(10) =8649a(11) =10404a(12) =12321a(13) =14400a(14) =16641a(15) =19044a(16) =21609a(17) =24336a(18) =27225a(19) =30276a(20) =33489a(21) =36864a(22) =40401a(23) =44100a(24) =47961a(25) =51984a(26) =56169a(27) =60516a(28) =65025a(29) =69696