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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 18 |
| 6 | 154 |
| 7 | 970 |
| 8 | 4862 |
| 9 | 20879 |
| 10 | 83672 |
| 11 | 353281 |
| 12 | 1773612 |
| 13 | 11060634 |
| 14 | 84779040 |
| 15 | 772415014 |
| 16 | 7726721969 |
| 17 | 77774342729 |
| 18 | 747754441850 |
| 19 | 6734769291340 |
| 20 | 56695273838174 |
| 21 | 448350981091266 |
| 22 | 3357088027977272 |
| 23 | 24017325363442968 |
[1,1,1,1,2,18,154,970,4862,20879,83672,353281, 1773612,11060634,84779040,772415014,7726721969, 77774342729,747754441850,6734769291340, 56695273838174,448350981091266,3357088027977272, 24017325363442968] |