a(n) = (11^n + 5^n)/2.

Terms

a(0) =1a(1) =8a(2) =73a(3) =728a(4) =7633a(5) =82088a(6) =893593a(7) =9782648a(8) =107374753a(9) =1179950408a(10) =12973595113a(11) =142680249368