# A067578 (b-file synthesized from sequence entry) 1 1 2 2 3 5 4 12 5 52 6 120 7 752 8 3200 9 19968 10 84480 11 863232 12 3637248 13 44384256 14 275152896 15 2254307328 16 18459131904 17 298743496704 18 1846819160064 19 33568893960192 20 274421835104256 21 3340027488632832 22 33963860494909440 23 752840786973818880 24 6146715129678397440 25 123926213264670720000