a(n) = n! / A003040(n).

Terms

a(0) =1a(1) =2a(2) =3a(3) =8a(4) =20a(5) =45a(6) =144a(7) =448a(8) =1680a(9) =4725a(10) =17280a(11) =62208a(12) =290304a(13) =1254400a(14) =4465125a(15) =18144000a(16) =72990720a(17) =391910400a(18) =1881169920a(19) =9754214400a(20) =45660160000a(21) =205752960000a(22) =905748480000