# A337010 (b-file synthesized from sequence entry) 0 1 1 4 2 18 3 92 4 532 5 3440 6 24552 7 191280 8 1612304 9 14597952 10 141123872 11 1449324992 12 15743376704 13 180203389696 14 2166381979264 15 27274611880704 16 358690234163456 17 4916123783848960 18 70076765972288000 19 1036967662211324928 20 15902394743591408640