# A052566 (b-file synthesized from sequence entry) 0 2 1 1 2 4 3 6 4 48 5 120 6 1440 7 5040 8 80640 9 362880 10 7257600 11 39916800 12 958003200 13 6227020800 14 174356582400 15 1307674368000 16 41845579776000 17 355687428096000 18 12804747411456000 19 121645100408832000 20 4865804016353280000 21 51090942171709440000 22 2248001455555215360000