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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 20 |
| 3 | 165 |
| 4 | 1520 |
| 5 | 14982 |
| 6 | 154588 |
| 7 | 1648713 |
| 8 | 18029456 |
| 9 | 201063402 |
| 10 | 2277890472 |
| 11 | 26143479954 |
| 12 | 303322798896 |
| 13 | 3551784992172 |
| 14 | 41920546809900 |
| 15 | 498190056106161 |
| 16 | 5956394533009520 |
| 17 | 71595959974620738 |
| 18 | 864682199472132376 |
| 19 | 10487531546082633270 |
| 20 | 127689839838217004000 |
[1,3,20,165,1520,14982,154588,1648713,18029456, 201063402,2277890472,26143479954,303322798896, 3551784992172,41920546809900,498190056106161, 5956394533009520,71595959974620738, 864682199472132376,10487531546082633270, 127689839838217004000] |