# A203151 (b-file synthesized from sequence entry) 1 1 2 2 3 5 4 12 5 40 6 132 7 564 8 2400 9 12576 10 65760 11 408960 12 2540160 13 18299520 14 131725440 15 1079205120 16 8836853760 17 81157386240 18 745047797760 19 7582159872000 20 77138417664000 21 861690783744000 22 9623448705024000 23 117074735382528000