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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 3 |
| 5 | 6 |
| 6 | 27 |
| 7 | 99 |
| 8 | 463 |
| 9 | 2232 |
| 10 | 11839 |
| 11 | 66176 |
| 12 | 390465 |
| 13 | 2394678 |
| 14 | 15154985 |
| 15 | 98121614 |
| 16 | 646053822 |
| 17 | 4304919741 |
| 18 | 28930077597 |
[1,1,1,3,6,27,99,463,2232,11839,66176,390465, 2394678,15154985,98121614,646053822,4304919741, 28930077597] |