a(n) = (9*n + 6)^2.

Terms

a(0) =36a(1) =225a(2) =576a(3) =1089a(4) =1764a(5) =2601a(6) =3600a(7) =4761a(8) =6084a(9) =7569a(10) =9216a(11) =11025a(12) =12996a(13) =15129a(14) =17424a(15) =19881a(16) =22500a(17) =25281a(18) =28224a(19) =31329a(20) =34596a(21) =38025a(22) =41616a(23) =45369a(24) =49284a(25) =53361a(26) =57600a(27) =62001a(28) =66564a(29) =71289