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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 20 |
| 4 | 56 |
| 5 | 320 |
| 6 | 1120 |
| 7 | 5312 |
| 8 | 20608 |
| 9 | 90880 |
| 10 | 368640 |
| 11 | 1577984 |
| 12 | 6522880 |
| 13 | 27578368 |
| 14 | 114909184 |
| 15 | 483328000 |
| 16 | 2020573184 |
| 17 | 8480555008 |
| 18 | 35502817280 |
| 19 | 148874461184 |
| 20 | 623609118720 |
| 21 | 2614000353280 |
| 22 | 10952269365248 |
| 23 | 45901678641152 |
| 24 | 192340840939520 |
[0,1,2,20,56,320,1120,5312,20608,90880,368640, 1577984,6522880,27578368,114909184,483328000, 2020573184,8480555008,35502817280,148874461184, 623609118720,2614000353280,10952269365248, 45901678641152,192340840939520] |