a(n) = 6^n + 7^n + 9^n.

Terms

a(0) =3a(1) =22a(2) =166a(3) =1288a(4) =10258a(5) =83632a(6) =695746a(7) =5886448a(8) =50491138a(9) =437851792a(10) =3829725826a(11) =33721183408a(12) =298447606018