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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 21 |
| 2 | 441 |
| 3 | 9872 |
| 4 | 220447 |
| 5 | 5247292 |
| 6 | 124278971 |
| 7 | 3113440755 |
| 8 | 77520962327 |
| 9 | 2024021927610 |
[1,21,441,9872,220447,5247292,124278971, 3113440755,77520962327,2024021927610] |