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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 464 |
| 7 | 2274 |
| 8 | 13236 |
| 9 | 91760 |
| 10 | 740562 |
| 11 | 6541984 |
| 12 | 65632694 |
| 13 | 732880076 |
| 14 | 8995905626 |
| 15 | 120367234946 |
[1,1,2,6,24,120,464,2274,13236,91760,740562, 6541984,65632694,732880076,8995905626, 120367234946] |