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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 18 |
| 6 | 54 |
| 7 | 166 |
| 8 | 522 |
| 9 | 1670 |
| 10 | 5418 |
| 11 | 17786 |
| 12 | 58974 |
| 13 | 197226 |
| 14 | 664494 |
| 15 | 2253390 |
| 16 | 7685394 |
| 17 | 26345230 |
| 18 | 90721362 |
| 19 | 313682098 |
| 20 | 1088609142 |
| 21 | 3790610306 |
| 22 | 13239554790 |
| 23 | 46371693174 |
| 24 | 162835695258 |
| 25 | 573160873750 |
| 26 | 2021885799162 |
| 27 | 7146955776554 |
[1,1,1,2,6,18,54,166,522,1670,5418,17786,58974, 197226,664494,2253390,7685394,26345230,90721362, 313682098,1088609142,3790610306,13239554790, 46371693174,162835695258,573160873750, 2021885799162,7146955776554] |