Number of connected ordered 2-element multiantichains on a labeled n-set.

Terms

a(0) =0a(1) =1a(2) =1a(3) =7a(4) =37a(5) =151a(6) =541a(7) =1807a(8) =5797a(9) =18151a(10) =55981a(11) =171007a(12) =519157a(13) =1569751a(14) =4733821a(15) =14250607a(16) =42850117a(17) =128746951a(18) =386634061a(19) =1160688607a(20) =3483638677a(21) =10454061751a(22) =31368476701a(23) =94118013007a(24) =282379204837a(25) =847187946151