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A055533 as a simple table

na(n)
21
312
4108
5960
69000
790720
8987840
911612160
10146966400
111995840000
1228979596800
13448345497600
147366565606400
15128152088064000
162353813862400000
1745527990796288000
18925143000477696000

[1,12,108,960,9000,90720,987840,11612160,
 146966400,1995840000,28979596800,448345497600,
 7366565606400,128152088064000,2353813862400000,
 45527990796288000,925143000477696000]