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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 20 |
| 4 | 103 |
| 5 | 899 |
| 6 | 8143 |
| 7 | 84678 |
| 8 | 975049 |
| 9 | 13082993 |
| 10 | 186340631 |
| 11 | 2878977408 |
| 12 | 48899305783 |
| 13 | 876721463435 |
| 14 | 16971889682707 |
| 15 | 349059348881834 |
| 16 | 7565120836998801 |
| 17 | 173313418321443809 |
| 18 | 4197655086606145387 |
| 19 | 106097089652021765356 |
| 20 | 2816940203630838490791 |
| 21 | 78147038018470085005235 |
[1,1,3,20,103,899,8143,84678,975049,13082993, 186340631,2878977408,48899305783,876721463435, 16971889682707,349059348881834,7565120836998801, 173313418321443809,4197655086606145387, 106097089652021765356,2816940203630838490791, 78147038018470085005235] |