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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 23 |
| 5 | 104 |
| 6 | 530 |
| 7 | 2959 |
| 8 | 17757 |
| 9 | 113000 |
| 10 | 754981 |
| 11 | 5255830 |
| 12 | 37898152 |
| 13 | 281717723 |
| 14 | 2150636759 |
| 15 | 16807757093 |
[1,1,2,6,23,104,530,2959,17757,113000,754981, 5255830,37898152,281717723,2150636759,16807757093] |