Numbers of the form (4^{mr}-1)/(4^r-1) for positive integers m, r.

Terms

a(0) =1a(1) =5a(2) =17a(3) =21a(4) =65a(5) =85a(6) =257a(7) =273a(8) =341a(9) =1025a(10) =1365a(11) =4097a(12) =4161a(13) =4369a(14) =5461a(15) =16385a(16) =21845a(17) =65537a(18) =65793a(19) =69905a(20) =87381a(21) =262145a(22) =266305a(23) =349525a(24) =1048577a(25) =1049601a(26) =1118481a(27) =1398101a(28) =4194305a(29) =5592405