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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 9 |
| 5 | 40 |
| 6 | 219 |
| 7 | 1441 |
| 8 | 10923 |
| 9 | 93755 |
| 10 | 898485 |
| 11 | 9508957 |
| 12 | 110145409 |
| 13 | 1385996397 |
| 14 | 18826451053 |
| 15 | 274552411176 |
| 16 | 4278441740821 |
| 17 | 70950825535271 |
| 18 | 1247552015661834 |
| 19 | 23183674957715737 |
| 20 | 454013634588599834 |
[1,1,1,3,9,40,219,1441,10923,93755,898485,9508957, 110145409,1385996397,18826451053,274552411176, 4278441740821,70950825535271,1247552015661834, 23183674957715737,454013634588599834] |