# A072489 (b-file synthesized from sequence entry) 1 1 2 2 3 6 4 12 5 60 6 180 7 1260 8 5040 9 15120 10 75600 11 831600 12 3326400 13 43243200 14 302702400 15 1513512000 16 6054048000 17 102918816000 18 617512896000 19 11732745024000 20 58663725120000