# A000553 (b-file synthesized from sequence entry) 5 120 6 2520 7 43680 8 757680 9 13747104 10 264181680 11 5395040640 12 117080049240 13 2696387899920 14 65774992411128 15 1695845836077120 16 46110625382246880 17 1319345179723609920 18 39640903618873667040 19 1248193457738661143808