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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 5 |
| 3 | 21 |
| 4 | 102 |
| 5 | 640 |
| 6 | 4492 |
| 7 | 34047 |
| 8 | 272252 |
| 9 | 2268085 |
| 10 | 19502386 |
| 11 | 172113886 |
| 12 | 1551948268 |
[1,2,5,21,102,640,4492,34047,272252,2268085, 19502386,172113886,1551948268] |