Duplicate of A069466.

Terms

a(0) =1a(1) =2a(2) =2a(3) =6a(4) =24a(5) =6a(6) =20a(7) =180a(8) =180a(9) =20a(10) =70a(11) =1120a(12) =2520a(13) =1120a(14) =70a(15) =252a(16) =6300a(17) =25200a(18) =25200a(19) =6300a(20) =252a(21) =924a(22) =33264a(23) =207900a(24) =369600a(25) =207900a(26) =33264a(27) =924a(28) =3432a(29) =168168