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A006157 as a simple table

na(n)
21
35
428
5180
61320
710920
8100800
91028160
1011491200
11139708800
121836172800
1325945920000
14392302310400
156320426112000
16108101081088000
171956280854528000
1837347179950080000
19750144785854464000
2015813863053148160000
21349121438173347840000

[1,5,28,180,1320,10920,100800,1028160,11491200,
 139708800,1836172800,25945920000,392302310400,
 6320426112000,108101081088000,1956280854528000,
 37347179950080000,750144785854464000,
 15813863053148160000,349121438173347840000]