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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 7 |
| 3 | 21 |
| 4 | 86 |
| 5 | 308 |
| 6 | 1334 |
| 7 | 5105 |
| 8 | 22767 |
| 9 | 91337 |
| 10 | 414498 |
| 11 | 1709124 |
| 12 | 7849083 |
| 13 | 33074337 |
| 14 | 153116559 |
| 15 | 654915363 |
| 16 | 3051009294 |
| 17 | 13214018558 |
| 18 | 61839195598 |
| 19 | 270363305206 |
| 20 | 1270075518621 |
| 21 | 5598259111518 |
| 22 | 26375004035402 |
| 23 | 117014793372506 |
| 24 | 552683257105742 |
| 25 | 2466159918289860 |
| 26 | 11671475968085655 |
| 27 | 52329157562856000 |
[1,2,7,21,86,308,1334,5105,22767,91337,414498, 1709124,7849083,33074337,153116559,654915363, 3051009294,13214018558,61839195598,270363305206, 1270075518621,5598259111518,26375004035402, 117014793372506,552683257105742,2466159918289860, 11671475968085655,52329157562856000] |