a(1) = 1. If a(n) is composite, a(n+1) = 2*a(n)+1; otherwise, a(n+1) = 2*a(n).

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =19a(5) =38a(6) =77a(7) =155a(8) =311a(9) =622a(10) =1245a(11) =2491a(12) =4983a(13) =9967a(14) =19934a(15) =39869a(16) =79738a(17) =159477a(18) =318955a(19) =637911a(20) =1275823a(21) =2551646a(22) =5103293a(23) =10206587a(24) =20413175a(25) =40826351a(26) =81652702a(27) =163305405a(28) =326610811a(29) =653221623