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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 8 |
| 5 | 36 |
| 6 | 180 |
| 7 | 1008 |
| 8 | 6336 |
| 9 | 46080 |
| 10 | 374400 |
| 11 | 3369600 |
| 12 | 32659200 |
| 13 | 344736000 |
| 14 | 3886444800 |
| 15 | 47348582400 |
| 16 | 611264102400 |
| 17 | 8442272563200 |
| 18 | 122595843686400 |
| 19 | 1890952003584000 |
| 20 | 30510694932480000 |
| 21 | 520011800985600000 |
| 22 | 9231875243458560000 |
| 23 | 172292221923655680000 |
[1,1,1,2,8,36,180,1008,6336,46080,374400,3369600, 32659200,344736000,3886444800,47348582400, 611264102400,8442272563200,122595843686400, 1890952003584000,30510694932480000, 520011800985600000,9231875243458560000, 172292221923655680000] |