# A038154 (b-file synthesized from sequence entry) 0 0 1 0 2 2 3 12 4 60 5 320 6 1950 7 13692 8 109592 9 986400 10 9864090 11 108505100 12 1302061332 13 16926797472 14 236975164790 15 3554627472060 16 56874039553200 17 966858672404672 18 17403456103284402 19 330665665962403980 20 6613313319248079980 21 138879579704209680000