a(n) = floor(d(n)/18^(n-1)) where d(n) = 0, 1, -8, 352, -5120,.. and d(n) = -8*d(n-1) +288*d(n-2).

Terms

a(0) =0a(1) =1a(2) =-1a(3) =1a(4) =-1a(5) =1a(6) =-2a(7) =1a(8) =-3a(9) =2a(10) =-3a(11) =3a(12) =-5a(13) =5a(14) =-6a(15) =7a(16) =-9a(17) =10a(18) =-12a(19) =14a(20) =-17a(21) =20a(22) =-25a(23) =28a(24) =-35a(25) =40a(26) =-49a(27) =57a(28) =-69a(29) =81