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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 13 |
| 5 | 36 |
| 6 | 181 |
| 7 | 848 |
| 8 | 3865 |
| 9 | 23824 |
| 10 | 140521 |
| 11 | 871872 |
| 12 | 6324517 |
| 13 | 44942912 |
| 14 | 344747677 |
| 15 | 2860930816 |
| 16 | 23853473329 |
| 17 | 213856723200 |
| 18 | 1996865965009 |
| 19 | 19099352929280 |
| 20 | 193406280000061 |
| 21 | 2010469524579328 |
| 22 | 21615227339380357 |
| 23 | 242177953175506944 |
[1,1,1,4,13,36,181,848,3865,23824,140521,871872, 6324517,44942912,344747677,2860930816,23853473329, 213856723200,1996865965009,19099352929280, 193406280000061,2010469524579328, 21615227339380357,242177953175506944] |