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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 1 |
| 4 | 9 |
| 5 | 24 |
| 6 | 94 |
| 7 | 870 |
| 8 | 7731 |
| 9 | 58940 |
| 10 | 1518701 |
| 11 | 25116276 |
| 12 | 780979887 |
| 13 | 31966477480 |
[1,2,1,9,24,94,870,7731,58940,1518701,25116276, 780979887,31966477480] |