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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 50 |
| 5 | 138 |
| 6 | 430 |
| 7 | 1242 |
| 8 | 3666 |
| 9 | 10938 |
| 10 | 34598 |
| 11 | 108098 |
| 12 | 338634 |
| 13 | 1058370 |
[1,2,6,18,50,138,430,1242,3666,10938,34598,108098, 338634,1058370] |