a(n) is the bitwise OR of (the binary expansions of) b(n+1) to b(2*n), where b is A354169.

Terms

a(0) =2a(1) =12a(2) =27a(3) =115a(4) =252a(5) =1004a(6) =2013a(7) =4031a(8) =16307a(9) =32631a(10) =65279a(11) =261375a(12) =524270a(13) =2096110a(14) =4194253a(15) =8386527a(16) =16773119a(17) =67096575a(18) =134217659a(19) =536854459a(20) =1073741623a(21) =2147450751a(22) =4294901759a(23) =17179672575a(24) =34359737599a(25) =137438690559a(26) =274877382143a(27) =549754765311