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) =63a(9) =125a(10) =249a(11) =496a(12) =988a(13) =1968a(14) =3920a(15) =7808a(16) =15552a(17) =30978a(18) =61705a(19) =122910a(20) =244824a(21) =487664a(22) =971376a(23) =1934880a(24) =3854082a(25) =7676935a(26) =15291665a(27) =30459424a(28) =60672040a(29) =120852464