Arises in enumerating Huffman codes, compact trees, and sums of unit fractions.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =8a(6) =16a(7) =32a(8) =64a(9) =127a(10) =253a(11) =505a(12) =1008a(13) =2012a(14) =4016a(15) =8016a(16) =16000a(17) =31936a(18) =63744a(19) =127234a(20) =253961a(21) =506910a(22) =1011800a(23) =2019568a(24) =4031088a(25) =8046112a(26) =16060160a(27) =32056322a(28) =63984903a(29) =127714833