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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 5 |
| 3 | 21 |
| 4 | 89 |
| 5 | 393 |
| 6 | 1805 |
| 7 | 8557 |
| 8 | 41585 |
| 9 | 206097 |
| 10 | 1037717 |
| 11 | 5293445 |
| 12 | 27297737 |
| 13 | 142078745 |
| 14 | 745387037 |
| 15 | 3937603037 |
| 16 | 20927156705 |
| 17 | 111818026017 |
| 18 | 600318853925 |
| 19 | 3236724317173 |
[0,1,5,21,89,393,1805,8557,41585,206097,1037717, 5293445,27297737,142078745,745387037,3937603037, 20927156705,111818026017,600318853925, 3236724317173] |