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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 25 |
| 6 | 137 |
| 7 | 521 |
| 8 | 6501 |
| 9 | 70441 |
| 10 | 694381 |
| 11 | 20946853 |
| 12 | 656540805 |
| 13 | 20990265609 |
[1,1,1,1,25,137,521,6501,70441,694381,20946853, 656540805,20990265609] |