Number of N- and bowtie-free posets with n elements.

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =40a(5) =121a(6) =373a(7) =1184a(8) =3823a(9) =12554a(10) =41733a(11) =140301a(12) =475934a(13) =1627440a(14) =5602983a(15) =19406703a(16) =67574371a(17) =236409625a(18) =830582851a(19) =2929246932a(20) =10366380583a(21) =36801225872a(22) =131021870786a(23) =467701875135