a(n) = 7^n + 8^n + 9^n.

Terms

a(0) =3a(1) =24a(2) =194a(3) =1584a(4) =13058a(5) =108624a(6) =911234a(7) =7703664a(8) =65588738a(9) =561991824a(10) =4843001474a(11) =41948320944a(12) =364990300418