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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 12 |
| 4 | 84 |
| 5 | 720 |
| 6 | 7320 |
| 7 | 85680 |
| 8 | 1130640 |
| 9 | 16571520 |
| 10 | 266747040 |
| 11 | 4673592000 |
| 12 | 88476252480 |
| 13 | 1798674958080 |
| 14 | 39061703640960 |
| 15 | 902110060051200 |
| 16 | 22068313153286400 |
| 17 | 569874634276147200 |
| 18 | 15486794507222438400 |
| 19 | 441703937156940057600 |
| 20 | 13189422568491333964800 |
| 21 | 411420697666247453184000 |
[1,0,2,12,84,720,7320,85680,1130640,16571520, 266747040,4673592000,88476252480,1798674958080, 39061703640960,902110060051200,22068313153286400, 569874634276147200,15486794507222438400, 441703937156940057600,13189422568491333964800, 411420697666247453184000] |