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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 17 |
| 4 | 66 |
| 5 | 247 |
| 6 | 918 |
| 7 | 3425 |
| 8 | 12862 |
| 9 | 48611 |
| 10 | 184746 |
| 11 | 705421 |
| 12 | 2704144 |
| 13 | 10400587 |
| 14 | 40116586 |
| 15 | 155117505 |
| 16 | 601080374 |
| 17 | 2333606203 |
| 18 | 9075135282 |
| 19 | 35345263781 |
| 20 | 137846528800 |
| 21 | 538257874419 |
| 22 | 2104098963698 |
| 23 | 8233430727577 |
| 24 | 32247603683076 |
[1,1,4,17,66,247,918,3425,12862,48611,184746, 705421,2704144,10400587,40116586,155117505, 601080374,2333606203,9075135282,35345263781, 137846528800,538257874419,2104098963698, 8233430727577,32247603683076] |