# 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