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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 17 |
| 6 | 180 |
| 7 | 1536 |
| 8 | 11616 |
| 9 | 81552 |
| 10 | 545536 |
| 11 | 3532544 |
| 12 | 22368000 |
| 13 | 139434240 |
| 14 | 859634688 |
| 15 | 5258379264 |
| 16 | 31986270208 |
| 17 | 193796182016 |
| 18 | 1170829049856 |
| 19 | 7059331547136 |
[0,0,0,0,1,17,180,1536,11616,81552,545536,3532544, 22368000,139434240,859634688,5258379264, 31986270208,193796182016,1170829049856, 7059331547136] |