a(n) = n!/A093888(n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =3a(5) =15a(6) =80a(7) =20a(8) =160a(9) =1440a(10) =75a(11) =825a(12) =9900a(13) =128700a(14) =165888a(15) =2488320a(16) =39813120a(17) =597196800a(18) =10749542400a(19) =125411328000