a(n) = 27*(n - 6)^2 + 4*(n - 6)^3 = ((n - 6)^2)*(4*n + 3).

Terms

a(0) =108a(1) =175a(2) =176a(3) =135a(4) =76a(5) =23a(6) =0a(7) =31a(8) =140a(9) =351a(10) =688a(11) =1175a(12) =1836a(13) =2695a(14) =3776a(15) =5103a(16) =6700a(17) =8591a(18) =10800a(19) =13351a(20) =16268a(21) =19575a(22) =23296a(23) =27455a(24) =32076a(25) =37183a(26) =42800a(27) =48951a(28) =55660a(29) =62951