# A055533 (b-file synthesized from sequence entry) 2 1 3 12 4 108 5 960 6 9000 7 90720 8 987840 9 11612160 10 146966400 11 1995840000 12 28979596800 13 448345497600 14 7366565606400 15 128152088064000 16 2353813862400000 17 45527990796288000 18 925143000477696000