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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 7 |
| 3 | 84 |
| 4 | 756 |
| 5 | 6048 |
| 6 | 45360 |
| 7 | 326592 |
| 8 | 2286144 |
| 9 | 15676416 |
| 10 | 105815808 |
| 11 | 705438720 |
| 12 | 4655895552 |
| 13 | 30474952704 |
| 14 | 198087192576 |
| 15 | 1279948013568 |
| 16 | 8228237230080 |
| 17 | 52660718272512 |
| 18 | 335712078987264 |
| 19 | 2132759090036736 |
| 20 | 13507474236899328 |
[0,7,84,756,6048,45360,326592,2286144,15676416, 105815808,705438720,4655895552,30474952704, 198087192576,1279948013568,8228237230080, 52660718272512,335712078987264,2132759090036736, 13507474236899328] |