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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 9 |
| 5 | 24 |
| 6 | 100 |
| 7 | 300 |
| 8 | 1225 |
| 9 | 3920 |
| 10 | 15876 |
| 11 | 52920 |
| 12 | 213444 |
| 13 | 731808 |
| 14 | 2944656 |
| 15 | 10306296 |
| 16 | 41409225 |
| 17 | 147232800 |
| 18 | 590976100 |
| 19 | 2127513960 |
| 20 | 8533694884 |
| 21 | 31031617760 |
| 22 | 124408576656 |
| 23 | 456164781072 |
| 24 | 1828114918084 |
| 25 | 6749962774464 |
| 26 | 27043120090000 |
| 27 | 100445874620000 |
| 28 | 402335398890000 |
[1,0,1,2,9,24,100,300,1225,3920,15876,52920, 213444,731808,2944656,10306296,41409225,147232800, 590976100,2127513960,8533694884,31031617760, 124408576656,456164781072,1828114918084, 6749962774464,27043120090000,100445874620000, 402335398890000] |