a(n) = 3^n + 8^n.

Terms

a(0) =2a(1) =11a(2) =73a(3) =539a(4) =4177a(5) =33011a(6) =262873a(7) =2099339a(8) =16783777a(9) =134237411a(10) =1073800873a(11) =8590111739a(12) =68720008177a(13) =549757408211