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| n | a(n) |
|---|---|
| 1 | 21 |
| 2 | 441 |
| 3 | 1889 |
| 4 | 6315 |
| 5 | 32823 |
| 6 | 138017 |
| 7 | 738515 |
| 8 | 3451393 |
| 9 | 18459985 |
| 10 | 91330863 |
| 11 | 487900273 |
| 12 | 2497699401 |
| 13 | 13360428739 |
| 14 | 69888755449 |
| 15 | 374927533581 |
| 16 | 1989044972519 |
| 17 | 10707046454737 |
| 18 | 57336073886865 |
| 19 | 309657266929019 |
| 20 | 1668728092514473 |
[21,441,1889,6315,32823,138017,738515,3451393, 18459985,91330863,487900273,2497699401, 13360428739,69888755449,374927533581, 1989044972519,10707046454737,57336073886865, 309657266929019,1668728092514473] |