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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 34 |
| 4 | 376 |
| 5 | 5896 |
| 6 | 107104 |
| 7 | 2445664 |
| 8 | 61835776 |
| 9 | 1853785216 |
| 10 | 60075541504 |
| 11 | 2229983878144 |
| 12 | 88157067006976 |
| 13 | 3901637972801536 |
| 14 | 182049480718741504 |
| 15 | 9356335870657921024 |
| 16 | 503257631887961522176 |
| 17 | 29455739077723718189056 |
| 18 | 1794347026494847887867904 |
| 19 | 117825990265521485020463104 |
[1,1,4,34,376,5896,107104,2445664,61835776, 1853785216,60075541504,2229983878144, 88157067006976,3901637972801536, 182049480718741504,9356335870657921024, 503257631887961522176,29455739077723718189056, 1794347026494847887867904, 117825990265521485020463104] |