# A024333 (b-file synthesized from sequence entry) 0 0 1 0 2 1 3 -3 4 11 5 -50 6 154 7 756 8 -25572 9 434736 10 -6324264 11 84312360 12 -1014504360 13 9750096720 14 -26179417200 15 -2263442045760 16 92224441646400 17 -2623899775526400 18 64132749053646720 19 -1393649719639125120 20 25953090802663939200 21 -339671851067737440000