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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 6 |
| 5 | 15 |
| 6 | 255 |
| 7 | 1897 |
| 8 | 92263 |
| 9 | 1972653 |
| 10 | 281035054 |
| 11 | 17635484470 |
| 12 | 7490694495750 |
| 13 | 1405083604458437 |
| 14 | 1789509008288411290 |
[1,1,1,6,15,255,1897,92263,1972653,281035054, 17635484470,7490694495750,1405083604458437, 1789509008288411290] |