a(n) = 4^n + 5^n + 9^n.

Terms

a(0) =3a(1) =18a(2) =122a(3) =918a(4) =7442a(5) =63198a(6) =551162a(7) =4877478a(8) =43502882a(9) =389635758a(10) =3497598602a(11) =31434082038a(12) =282690454322