Number of rooted twice-partitions of n.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =8a(5) =15a(6) =30a(7) =54a(8) =103a(9) =186a(10) =345a(11) =606a(12) =1115a(13) =1936a(14) =3466a(15) =6046a(16) =10630a(17) =18257a(18) =31927a(19) =54393a(20) =93894a(21) =159631a(22) =272155a(23) =458891a(24) =779375a(25) =1305801a(26) =2196009a(27) =3667242a(28) =6130066a(29) =10170745