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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 1 |
| 6 | 5 |
| 7 | 17 |
| 8 | 39 |
| 9 | 143 |
| 10 | 759 |
| 11 | 4705 |
| 12 | 36573 |
| 13 | 332389 |
| 14 | 3601255 |
| 15 | 48371515 |
| 16 | 827745175 |
| 17 | 17238229681 |
| 18 | 441854255629 |
| 19 | 13777843130457 |
| 20 | 527986032874649 |
| 21 | 24769703202602783 |
[1,1,1,1,1,5,17,39,143,759,4705,36573,332389, 3601255,48371515,827745175,17238229681, 441854255629,13777843130457,527986032874649, 24769703202602783] |