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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 5 |
| 2 | 25 |
| 3 | 120 |
| 4 | 580 |
| 5 | 2800 |
| 6 | 13500 |
| 7 | 65100 |
| 8 | 313940 |
| 9 | 1513820 |
| 10 | 7299760 |
| 11 | 35200020 |
| 12 | 169736780 |
| 13 | 818482260 |
| 14 | 3946776920 |
| 15 | 19031623000 |
[1,5,25,120,580,2800,13500,65100,313940,1513820, 7299760,35200020,169736780,818482260,3946776920, 19031623000] |