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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 6 |
| 3 | 6 |
| 4 | 630 |
| 5 | 1398 |
| 6 | 93672 |
| 7 | 609264 |
| 8 | 20702760 |
| 9 | 279681294 |
| 10 | 7420195854 |
| 11 | 149049265998 |
| 12 | 3763960753368 |
| 13 | 88917911372016 |
[0,6,6,630,1398,93672,609264,20702760,279681294, 7420195854,149049265998,3763960753368, 88917911372016] |