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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 8 |
| 5 | 28 |
| 6 | 143 |
| 7 | 747 |
| 8 | 4346 |
| 9 | 25974 |
| 10 | 160869 |
| 11 | 1015723 |
| 12 | 6531611 |
| 13 | 42592880 |
[1,1,1,2,8,28,143,747,4346,25974,160869,1015723, 6531611,42592880] |