a(n) = a(n-1) + 8*a(n-2) for n >= 2, a(0)=1, a(1)=2.

Terms

a(0) =1a(1) =2a(2) =10a(3) =26a(4) =106a(5) =314a(6) =1162a(7) =3674a(8) =12970a(9) =42362a(10) =146122a(11) =485018a(12) =1653994a(13) =5534138a(14) =18766090a(15) =63039194a(16) =213167914a(17) =717481466a(18) =2422824778a(19) =8162676506a(20) =27545274730a(21) =92846686778a(22) =313208884618