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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 20 |
| 7 | 210 |
| 8 | 1960 |
| 9 | 18900 |
| 10 | 194880 |
| 11 | 2166780 |
| 12 | 26356880 |
| 13 | 349806600 |
| 14 | 5029088064 |
| 15 | 77748751080 |
| 16 | 1284349422720 |
| 17 | 22551300670080 |
| 18 | 419191223208384 |
| 19 | 8222848137607680 |
| 20 | 169760091173740800 |
| 21 | 3679746265902067200 |
| 22 | 83564915096633308800 |
| 23 | 1984162781781147770880 |
[1,0,0,0,0,0,20,210,1960,18900,194880,2166780, 26356880,349806600,5029088064,77748751080, 1284349422720,22551300670080,419191223208384, 8222848137607680,169760091173740800, 3679746265902067200,83564915096633308800, 1984162781781147770880] |