# A004824 (b-file synthesized from sequence entry)
1 1
2 1
3 1
4 3
5 36
6 900
7 675
8 66150
9 6350400
10 34292160
11 857304000
12 12966723000
13 222286680000
14 2366686281960000
15 57983813908020000
16 1581376742946000000
17 2226578454067968000000
18 55155529133626521600000
19 114553791277532006400000
20 3490915210814660428800000