# A181121 (b-file synthesized from sequence entry) 1 2 2 3 3 12 4 15 5 70 6 840 7 1260 8 2772 9 30030 10 720720 11 765765 12 12932920 13 243374040 14 6692786100 15 40156716600 16 83181770100 17 2406725881560 18 144403552893600 19 148414762696200 20 5476504743489780 21 224275908542914800