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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 4 |
| 5 | 16 |
| 6 | 80 |
| 7 | 672 |
| 8 | 4896 |
| 9 | 49920 |
| 10 | 460032 |
| 11 | 5598720 |
| 12 | 62584320 |
| 13 | 885381120 |
| 14 | 11644323840 |
| 15 | 187811205120 |
| 16 | 2841958748160 |
| 17 | 51481298534400 |
| 18 | 881192033648640 |
| 19 | 17714783352913920 |
| 20 | 338434210452602880 |
| 21 | 7477275543168614400 |
[1,0,0,0,4,16,80,672,4896,49920,460032,5598720, 62584320,885381120,11644323840,187811205120, 2841958748160,51481298534400,881192033648640, 17714783352913920,338434210452602880, 7477275543168614400] |