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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 9 |
| 5 | 34 |
| 6 | 140 |
| 7 | 672 |
| 8 | 4752 |
| 9 | 32304 |
| 10 | 230832 |
| 11 | 1780704 |
| 12 | 17927568 |
| 13 | 175473216 |
| 14 | 1780206336 |
| 15 | 18988867584 |
| 16 | 248341303296 |
| 17 | 3173837230080 |
| 18 | 41713375334400 |
| 19 | 568818754560000 |
| 20 | 9150176586240000 |
| 21 | 144343174487040000 |
| 22 | 2329812142295040000 |
[1,1,2,9,34,140,672,4752,32304,230832,1780704, 17927568,175473216,1780206336,18988867584, 248341303296,3173837230080,41713375334400, 568818754560000,9150176586240000, 144343174487040000,2329812142295040000] |