a(n) = 324*n^2 - 564*n + 321 (n>=1).

Terms

a(0) =81a(1) =489a(2) =1545a(3) =3249a(4) =5601a(5) =8601a(6) =12249a(7) =16545a(8) =21489a(9) =27081a(10) =33321a(11) =40209a(12) =47745a(13) =55929a(14) =64761a(15) =74241a(16) =84369a(17) =95145a(18) =106569a(19) =118641a(20) =131361a(21) =144729a(22) =158745a(23) =173409a(24) =188721a(25) =204681a(26) =221289a(27) =238545a(28) =256449a(29) =275001