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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 25 |
| 4 | 129 |
| 5 | 771 |
| 6 | 5172 |
| 7 | 38280 |
| 8 | 308987 |
| 9 | 2695586 |
| 10 | 25231269 |
| 11 | 251869681 |
| 12 | 2667876382 |
| 13 | 29856632341 |
| 14 | 351717286357 |
| 15 | 4347357161694 |
| 16 | 56222019376378 |
| 17 | 758836553993985 |
| 18 | 10665452531786380 |
| 19 | 155785594704483911 |
[1,2,6,25,129,771,5172,38280,308987,2695586, 25231269,251869681,2667876382,29856632341, 351717286357,4347357161694,56222019376378, 758836553993985,10665452531786380, 155785594704483911] |