# A166741 (b-file synthesized from sequence entry) 0 1 1 2 2 4 3 10 4 32 5 130 6 640 7 3770 8 25600 9 199810 10 1740800 11 16983850 12 181043200 13 2122981250 14 26794393600 15 367275756250 16 5358878720000 17 84106148181250 18 1393308467200000 19 24643101417106250 20 457005177241600000