a(n) = 5^n + 6^n + 9^n.

Terms

a(0) =3a(1) =20a(2) =142a(3) =1070a(4) =8482a(5) =69950a(6) =593722a(7) =5141030a(8) =45116962a(9) =399451310a(10) =3557016202a(11) =31792684790a(12) =284850459442