a(n) = 8^n+5^n-1.

Terms

a(0) =1a(1) =12a(2) =88a(3) =636a(4) =4720a(5) =35892a(6) =277768a(7) =2175276a(8) =17167840a(9) =136170852a(10) =1083507448a(11) =8638762716a(12) =68963617360a(13) =550976517012