Number of unlabeled P-series with n elements.

Terms

a(0) =1a(1) =2a(2) =5a(3) =13a(4) =31a(5) =76a(6) =178a(7) =423a(8) =988a(9) =2312a(10) =5361a(11) =12427a(12) =28626a(13) =65813a(14) =150700a(15) =344232a(16) =783832a(17) =1780650a(18) =4034591a(19) =9121571a(20) =20576349a(21) =46322816a(22) =104079338a(23) =233421517a(24) =522574991a(25) =1167974002a(26) =2606282841a(27) =5806953923a(28) =12919314397a(29) =28702716868