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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 18 |
| 3 | 660 |
| 4 | 42000 |
| 5 | 4142880 |
| 6 | 586776960 |
| 7 | 113020427520 |
| 8 | 28432576972800 |
| 9 | 9056055981772800 |
| 10 | 3562946373482496000 |
| 11 | 1697172166720622592000 |
| 12 | 962691052768668647424000 |
| 13 | 641260394342965606809600000 |
| 14 | 495681727573700350908825600000 |
| 15 | 440084864982859007245221888000000 |
[1,18,660,42000,4142880,586776960,113020427520, 28432576972800,9056055981772800, 3562946373482496000,1697172166720622592000, 962691052768668647424000, 641260394342965606809600000, 495681727573700350908825600000, 440084864982859007245221888000000] |