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A173499 as a simple table

na(n)
10
20
32
420
5204
62604
739990
8720600
914913080
10348678440
119090909090
12261535698060
138230246567620
14281241170407092
1510371206370520814
16410525522232055664
1717361641481138401520
18781282469559318055056

[0,0,2,20,204,2604,39990,720600,14913080,
 348678440,9090909090,261535698060,8230246567620,
 281241170407092,10371206370520814,
 410525522232055664,17361641481138401520,
 781282469559318055056]