a(n) = 27*n^2 - 21*n + 6 (n>=1).

Terms

a(0) =12a(1) =72a(2) =186a(3) =354a(4) =576a(5) =852a(6) =1182a(7) =1566a(8) =2004a(9) =2496a(10) =3042a(11) =3642a(12) =4296a(13) =5004a(14) =5766a(15) =6582a(16) =7452a(17) =8376a(18) =9354a(19) =10386a(20) =11472a(21) =12612a(22) =13806a(23) =15054a(24) =16356a(25) =17712a(26) =19122a(27) =20586a(28) =22104a(29) =23676