# A354851 (b-file synthesized from sequence entry) 1 1 2 3 3 8 4 54 5 144 6 2880 7 5760 8 206640 9 1491840 10 24675840 11 43545600 12 10298534400 13 6706022400 14 1195587993600 15 33476463820800 16 775450900224000 17 376610217984000 18 553805325545472000 19 128047474114560000 20 339876410542276608000 21 6208765924866785280000