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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 120 |
| 5 | 1320 |
| 6 | 17640 |
| 7 | 304920 |
| 8 | 6249600 |
| 9 | 143579520 |
| 10 | 3711052800 |
| 11 | 107762054400 |
| 12 | 3455138332800 |
| 13 | 120802387305600 |
| 14 | 4583177081683200 |
| 15 | 187766031131078400 |
| 16 | 8256125218115174400 |
| 17 | 387662886088250572800 |
| 18 | 19364540503274942976000 |
| 19 | 1025507260911983244595200 |
[1,1,2,12,120,1320,17640,304920,6249600,143579520, 3711052800,107762054400,3455138332800, 120802387305600,4583177081683200, 187766031131078400,8256125218115174400, 387662886088250572800,19364540503274942976000, 1025507260911983244595200] |