a(n) = 1 + (n-6)*2^(n-1).

Terms

a(0) =1a(1) =65a(2) =257a(3) =769a(4) =2049a(5) =5121a(6) =12289a(7) =28673a(8) =65537a(9) =147457a(10) =327681a(11) =720897a(12) =1572865a(13) =3407873a(14) =7340033a(15) =15728641a(16) =33554433a(17) =71303169a(18) =150994945a(19) =318767105a(20) =671088641a(21) =1409286145a(22) =2952790017a(23) =6174015489a(24) =12884901889a(25) =26843545601a(26) =55834574849a(27) =115964116993