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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 16 |
| 4 | 312 |
| 5 | 7552 |
| 6 | 220800 |
| 7 | 7597824 |
| 8 | 301321216 |
| 9 | 13545271296 |
| 10 | 681015214080 |
| 11 | 37879390720000 |
| 12 | 2309968030334976 |
| 13 | 153275504883695616 |
| 14 | 10995166075754119168 |
| 15 | 847974316241667686400 |
| 16 | 69971459959477921382400 |
| 17 | 6151490510604350965940224 |
| 18 | 574035430519008722436489216 |
| 19 | 56669921387839814123670994944 |
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