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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 36 |
| 4 | 432 |
| 5 | 6480 |
| 6 | 116640 |
| 7 | 2449440 |
| 8 | 58786560 |
| 9 | 1587237120 |
| 10 | 47617113600 |
| 11 | 1571364748800 |
| 12 | 56569130956800 |
| 13 | 2206196107315200 |
| 14 | 92660236507238400 |
| 15 | 4169710642825728000 |
| 16 | 200146110855634944000 |
| 17 | 10207451653637382144000 |
[0,1,4,36,432,6480,116640,2449440,58786560, 1587237120,47617113600,1571364748800, 56569130956800,2206196107315200,92660236507238400, 4169710642825728000,200146110855634944000, 10207451653637382144000] |