Numbers of the form 2^k+1 or 4^k-2^k+1.

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =9a(5) =13a(6) =17a(7) =33a(8) =57a(9) =65a(10) =129a(11) =241a(12) =257a(13) =513a(14) =993a(15) =1025a(16) =2049a(17) =4033a(18) =4097a(19) =8193a(20) =16257a(21) =16385a(22) =32769a(23) =65281a(24) =65537a(25) =131073a(26) =261633a(27) =262145a(28) =524289a(29) =1047553