# A137730 (b-file synthesized from sequence entry) 1 1 2 1 3 7 4 72 5 1452 6 43200 7 1814760 8 101606400 9 7315680960 10 658409472000 11 72425043734400 12 9560105533440000 13 1491376463456140800 14 271430516305428480000 15 57000408424183569945600 16 13680098021793595392000000 17 3720986661927868408018944000 18 1138621918549924531666944000000