a(n) = (2^n+3)^2-8.

Terms

a(0) =8a(1) =17a(2) =41a(3) =113a(4) =353a(5) =1217a(6) =4481a(7) =17153a(8) =67073a(9) =265217a(10) =1054721a(11) =4206593a(12) =16801793a(13) =67158017a(14) =268533761a(15) =1073938433a(16) =4295360513a(17) =17180655617a(18) =68721049601a(19) =274881052673