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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 21 |
| 4 | 1093 |
| 5 | 172217 |
| 6 | 81613877 |
| 7 | 113899763795 |
| 8 | 468482952092893 |
| 9 | 5676720267644621509 |
[0,1,21,1093,172217,81613877,113899763795, 468482952092893,5676720267644621509] |