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) =31a(8) =61a(9) =121a(10) =240a(11) =476a(12) =944a(13) =1872a(14) =3712a(15) =7362a(16) =14601a(17) =28958a(18) =57432a(19) =113904a(20) =225904a(21) =448034a(22) =888583a(23) =1762321a(24) =3495200a(25) =6932008a(26) =13748208a(27) =27266738a(28) =54077957a(29) =107252486