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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 16 |
| 6 | 56 |
| 7 | 408 |
| 8 | 2376 |
| 9 | 19920 |
| 10 | 156096 |
| 11 | 1711680 |
| 12 | 16851072 |
| 13 | 216434304 |
| 14 | 2557907712 |
| 15 | 38102969088 |
[1,1,2,4,16,56,408,2376,19920,156096,1711680, 16851072,216434304,2557907712,38102969088] |