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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 23 |
| 4 | 109 |
| 5 | 621 |
| 6 | 4149 |
| 7 | 31851 |
| 8 | 276408 |
| 9 | 2676388 |
| 10 | 28608866 |
| 11 | 334647768 |
| 12 | 4252140022 |
| 13 | 58322409086 |
| 14 | 858871301034 |
[1,2,6,23,109,621,4149,31851,276408,2676388, 28608866,334647768,4252140022,58322409086, 858871301034] |