a(n) = A002034(n)!/n.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =24a(5) =1a(6) =720a(7) =3a(8) =80a(9) =12a(10) =3628800a(11) =2a(12) =479001600a(13) =360a(14) =8a(15) =45a(17) =40a(19) =6a(20) =240a(21) =1814400a(23) =1a(24) =145152a(25) =239500800a(26) =13440a(27) =180