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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 7 |
| 3 | 55 |
| 4 | 571 |
| 5 | 7026 |
| 6 | 98925 |
| 7 | 1562219 |
| 8 | 27214867 |
| 9 | 516646333 |
| 10 | 10589130223 |
| 11 | 232574622116 |
| 12 | 5440521381816 |
| 13 | 134859301929873 |
| 14 | 3527034780915985 |
| 15 | 96965997588549555 |
| 16 | 2793286163779275779 |
| 17 | 84076751617833902070 |
| 18 | 2637677096916448507104 |
[1,1,7,55,571,7026,98925,1562219,27214867, 516646333,10589130223,232574622116,5440521381816, 134859301929873,3527034780915985, 96965997588549555,2793286163779275779, 84076751617833902070,2637677096916448507104] |