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| n | a(n) |
|---|---|
| 1 | 81 |
| 2 | 558 |
| 3 | 3888 |
| 4 | 27000 |
| 5 | 187704 |
| 6 | 1304424 |
| 7 | 9066168 |
| 8 | 63009576 |
| 9 | 437922936 |
| 10 | 3043586664 |
| 11 | 21153140280 |
| 12 | 147015651240 |
| 13 | 1021768400376 |
| 14 | 7101356197608 |
| 15 | 49354885831608 |
| 16 | 343019647846440 |
| 17 | 2384008752240504 |
| 18 | 16569015064994664 |
| 19 | 115155726797070648 |
[81,558,3888,27000,187704,1304424,9066168, 63009576,437922936,3043586664,21153140280, 147015651240,1021768400376,7101356197608, 49354885831608,343019647846440,2384008752240504, 16569015064994664,115155726797070648] |