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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 698 |
| 7 | 4393 |
| 8 | 28551 |
| 9 | 187403 |
| 10 | 1231517 |
| 11 | 8080058 |
| 12 | 52905865 |
| 13 | 345820994 |
[1,1,2,6,24,120,698,4393,28551,187403,1231517, 8080058,52905865,345820994] |