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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 9 |
| 3 | 55 |
| 4 | 369 |
| 5 | 2526 |
| 6 | 17577 |
| 7 | 123810 |
| 8 | 879921 |
| 9 | 6297643 |
| 10 | 45325764 |
| 11 | 327720471 |
| 12 | 2378598885 |
| 13 | 17319785588 |
| 14 | 126463925310 |
| 15 | 925620561780 |
| 16 | 6789081127137 |
| 17 | 49887667836693 |
| 18 | 367189338574827 |
| 19 | 2706613194698783 |
| 20 | 19977334121704344 |
| 21 | 147628150691297100 |
[1,1,9,55,369,2526,17577,123810,879921,6297643, 45325764,327720471,2378598885,17319785588, 126463925310,925620561780,6789081127137, 49887667836693,367189338574827,2706613194698783, 19977334121704344,147628150691297100] |