Number of (n+floor(n/2))-block bicoverings of an n-set.

Terms

a(0) =1a(1) =0a(2) =1a(3) =4a(4) =3a(5) =40a(6) =15a(7) =420a(8) =105a(9) =5040a(10) =945a(11) =69300a(12) =10395a(13) =1081080a(14) =135135a(15) =18918900a(16) =2027025a(17) =367567200a(18) =34459425a(19) =7856748900a(20) =654729075a(21) =183324141000a(22) =13749310575a(24) =316234143225