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) =128a(10) =255a(11) =509a(12) =1017a(13) =2032a(14) =4060a(15) =8112a(16) =16208a(17) =32384a(18) =64704a(19) =129280a(20) =258304a(21) =516098a(22) =1031177a(23) =2060318a(24) =4116568a(25) =8225008a(26) =16433776a(27) =32835104a(28) =65605376a(29) =131081216