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) =256a(11) =511a(12) =1021a(13) =2041a(14) =4080a(15) =8156a(16) =16304a(17) =32592a(18) =65152a(19) =130240a(20) =260352a(21) =520448a(22) =1040384a(23) =2079746a(24) =4157449a(25) =8310814a(26) =16613464a(27) =33210608a(28) =66388592a(29) =132711968