Number of unlabeled disconnected P-series with n elements.

Terms

a(0) =0a(1) =1a(2) =2a(3) =6a(4) =16a(5) =45a(6) =115a(7) =296a(8) =733a(9) =1801a(10) =4338a(11) =10380a(12) =24531a(13) =57622a(14) =134317a(15) =311465a(16) =718297a(17) =1649579a(18) =3772448a(19) =8597284a(20) =19527774a(21) =44225665a(22) =99885035a(23) =225032910a(24) =505797776a(25) =1134419571a(26) =2539173978a(27) =5672736196a(28) =12650878942a(29) =28165845957