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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 5 |
| 5 | 18 |
| 6 | 81 |
| 7 | 480 |
| 8 | 3874 |
| 9 | 39866 |
| 10 | 497818 |
| 11 | 7187627 |
| 12 | 116349635 |
| 13 | 2072540352 |
[1,0,1,2,5,18,81,480,3874,39866,497818,7187627, 116349635,2072540352] |