Duplicate of A060777.

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =12a(5) =30a(6) =72a(7) =210a(8) =630a(9) =1920a(10) =6336a(11) =22176a(12) =78975a(13) =295680a(14) =1144000a(15) =4576000