Number of purely crossing + partitions of [n].

Terms

a(0) =1a(1) =1a(2) =0a(3) =0a(4) =1a(5) =1a(6) =5a(7) =19a(8) =76a(9) =360a(10) =1792a(11) =9634a(12) =55286a(13) =336396a(14) =2162554a(15) =14629720a(16) =103818489a(17) =770678553a(18) =5969822993a(19) =48148947503a(20) =403545713463