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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 1 |
| 4 | 2 |
| 5 | 8 |
| 6 | 36 |
| 7 | 198 |
| 8 | 1272 |
| 9 | 9384 |
| 10 | 78240 |
| 11 | 728040 |
| 12 | 7482960 |
| 13 | 84224160 |
| 14 | 1030569120 |
| 15 | 13623366960 |
| 16 | 193515477120 |
| 17 | 2939860748160 |
| 18 | 47568519613440 |
| 19 | 816772822750080 |
| 20 | 14833749363552000 |
| 21 | 284114908317542400 |
| 22 | 5723753780712844800 |
| 23 | 120995656719515424000 |
| 24 | 2678008828724659584000 |
[1,0,1,2,8,36,198,1272,9384,78240,728040,7482960, 84224160,1030569120,13623366960,193515477120, 2939860748160,47568519613440,816772822750080, 14833749363552000,284114908317542400, 5723753780712844800,120995656719515424000, 2678008828724659584000] |