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A109923 as a simple table

na(n)
21
34
415
5420
63960
780080
81225224
919399380
105354228880
11145568097675
127600186994400
13254425307479200
149957281351799600
15392482839950100900
16114779426083185063200
175474978624167927514640
18312603618218620377448800

[1,4,15,420,3960,80080,1225224,19399380,
 5354228880,145568097675,7600186994400,
 254425307479200,9957281351799600,
 392482839950100900,114779426083185063200,
 5474978624167927514640,312603618218620377448800]