a(n) = 3^n + 2^(2*n + 1).

Terms

a(0) =11a(1) =41a(2) =155a(3) =593a(4) =2291a(5) =8921a(6) =34955a(7) =137633a(8) =543971a(9) =2156201a(10) =8565755a(11) =34085873a(12) =135812051a(13) =541653881a(14) =2161832555a(15) =8632981313a(16) =34488878531a(17) =137826373961a(18) =550918075355