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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 16 |
| 4 | 120 |
| 5 | 960 |
| 6 | 8400 |
| 7 | 80640 |
| 8 | 846720 |
| 9 | 9676800 |
| 10 | 119750400 |
| 11 | 1596672000 |
| 12 | 22832409600 |
| 13 | 348713164800 |
| 14 | 5666588928000 |
| 15 | 97639686144000 |
| 16 | 1778437140480000 |
| 17 | 34145993097216000 |
| 18 | 689322235650048000 |
| 19 | 14597412049059840000 |
| 20 | 323575967087493120000 |
| 21 | 7493338185184051200000 |
[0,2,16,120,960,8400,80640,846720,9676800, 119750400,1596672000,22832409600,348713164800, 5666588928000,97639686144000,1778437140480000, 34145993097216000,689322235650048000, 14597412049059840000,323575967087493120000, 7493338185184051200000] |