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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 24 |
| 4 | 228 |
| 5 | 2400 |
| 6 | 30360 |
| 7 | 453600 |
| 8 | 7702800 |
| 9 | 144910080 |
| 10 | 2981089440 |
| 11 | 66561264000 |
| 12 | 1603358729280 |
| 13 | 41434803970560 |
| 14 | 1142808612865920 |
| 15 | 33485770103385600 |
| 16 | 1038238875100627200 |
| 17 | 33945895488708403200 |
| 18 | 1166858228814204326400 |
| 19 | 42055660151648798054400 |
[1,0,2,24,228,2400,30360,453600,7702800,144910080, 2981089440,66561264000,1603358729280, 41434803970560,1142808612865920,33485770103385600, 1038238875100627200,33945895488708403200, 1166858228814204326400,42055660151648798054400] |