# A002698 (b-file synthesized from sequence entry)
2 1
3 18
4 160
5 1120
6 6912
7 39424
8 212992
9 1105920
10 5570560
11 27394048
12 132120576
13 627048448
14 2936012800
15 13589544960
16 62277025792
17 282930970624
18 1275605286912
19 5712306503680
20 25426206392320
21 112562502893568
22 495879744126976
23 2174833999740928
24 9499780463984640