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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 2 |
| 5 | 5 |
| 6 | 22 |
| 7 | 90 |
| 8 | 616 |
| 9 | 4988 |
| 10 | 46883 |
| 11 | 493406 |
| 12 | 5712809 |
| 13 | 71909602 |
[1,0,0,1,2,5,22,90,616,4988,46883,493406,5712809, 71909602] |