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A304561 as a simple table

na(n)
20
33
412
580
6840
7630
813440
9277200
1075600
113326400
12116839800
1316216200
141210809600
1565043178200
165448643200
17617512896000
1847147109609600
192639867630400
20422378820864000
2143505018548992000
221742312636064000
23374016445875072000
2449991305310266320000
251502744648605200000

[0,3,12,80,840,630,13440,277200,75600,3326400,
 116839800,16216200,1210809600,65043178200,
 5448643200,617512896000,47147109609600,
 2639867630400,422378820864000,43505018548992000,
 1742312636064000,374016445875072000,
 49991305310266320000,1502744648605200000]