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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 6 |
| 5 | 35 |
| 6 | 215 |
| 7 | 1414 |
| 8 | 9912 |
| 9 | 73324 |
| 10 | 565170 |
| 11 | 4472226 |
| 12 | 35725426 |
| 13 | 283350132 |
| 14 | 2225790476 |
| 15 | 18624038224 |
| 16 | 216679183120 |
| 17 | 4293834561200 |
| 18 | 111300845967440 |
| 19 | 2963219043255360 |
| 20 | 76258914698507280 |
| 21 | 1895550595605889760 |
| 22 | 45928558583373219600 |
| 23 | 1093984400513512753840 |
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