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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 7 |
| 4 | 26 |
| 5 | 124 |
| 6 | 640 |
| 7 | 3695 |
| 8 | 23231 |
| 9 | 156572 |
| 10 | 1133838 |
| 11 | 8635777 |
| 12 | 70212042 |
[1,1,2,7,26,124,640,3695,23231,156572,1133838, 8635777,70212042] |