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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 756 |
| 4 | 11197440 |
| 5 | 25328684620800 |
| 6 | 14303252551164700262400 |
| 7 | 2979637719108524426779310260224000 |
[0,4,756,11197440,25328684620800, 14303252551164700262400, 2979637719108524426779310260224000] |