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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 21 |
| 2 | 135 |
| 3 | 889 |
| 4 | 5903 |
| 5 | 39389 |
| 6 | 263647 |
| 7 | 1768457 |
| 8 | 11880131 |
| 9 | 79895207 |
| 10 | 537729241 |
| 11 | 3621234957 |
| 12 | 24396753479 |
| 13 | 164414536077 |
| 14 | 1108268954317 |
| 15 | 7471720473245 |
| 16 | 50378750794147 |
| 17 | 339712511249557 |
| 18 | 2290882896563443 |
| 19 | 15449485988902675 |
[1,21,135,889,5903,39389,263647,1768457,11880131, 79895207,537729241,3621234957,24396753479, 164414536077,1108268954317,7471720473245, 50378750794147,339712511249557,2290882896563443, 15449485988902675] |