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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 9 |
| 4 | 26 |
| 5 | 103 |
| 6 | 542 |
| 7 | 3529 |
| 8 | 26901 |
| 9 | 232416 |
| 10 | 2233500 |
| 11 | 23576045 |
| 12 | 270690473 |
| 13 | 3353312672 |
| 14 | 44520193362 |
| 15 | 629960268107 |
| 16 | 9456454463204 |
| 17 | 149995788999117 |
| 18 | 2505304374275816 |
| 19 | 43928236200319751 |
| 20 | 806397434192280456 |
[1,2,4,9,26,103,542,3529,26901,232416,2233500, 23576045,270690473,3353312672,44520193362, 629960268107,9456454463204,149995788999117, 2505304374275816,43928236200319751, 806397434192280456] |