Number of crossing partitions of {1,2,...,n} that contain no singletons.

A247491

Number of crossing partitions of {1,2,...,n} that contain no singletons.

Terms

    a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =5a(6) =26a(7) =126a(8) =624a(9) =3193a(10) =17119a(11) =96668a(12) =576104a(13) =3621982a(14) =23980620a(15) =166805068a(16) =1215842905a(17) =9263445775a(18) =73599067250a(19) =608471202527

External references