a(n) = 5^n + 8^n.

Terms

a(0) =2a(1) =13a(2) =89a(3) =637a(4) =4721a(5) =35893a(6) =277769a(7) =2175277a(8) =17167841a(9) =136170853a(10) =1083507449a(11) =8638762717a(12) =68963617361a(13) =550976517013