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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 15 |
| 5 | 69 |
| 6 | 389 |
| 7 | 2594 |
| 8 | 19884 |
| 9 | 172328 |
| 10 | 1665838 |
| 11 | 17768938 |
| 12 | 207304278 |
| 13 | 2625854188 |
| 14 | 35886673906 |
| 15 | 526337883960 |
| 16 | 8245960182038 |
| 17 | 137432669700634 |
| 18 | 2427977164711192 |
| 19 | 45322240407942258 |
| 20 | 891337394689531069 |
[1,1,2,4,15,69,389,2594,19884,172328,1665838, 17768938,207304278,2625854188,35886673906, 526337883960,8245960182038,137432669700634, 2427977164711192,45322240407942258, 891337394689531069] |