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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 36 |
| 3 | 135 |
| 4 | 620 |
| 5 | 3637 |
| 6 | 17450 |
| 7 | 86139 |
| 8 | 451210 |
| 9 | 2267574 |
| 10 | 11420744 |
| 11 | 58323254 |
| 12 | 295406628 |
| 13 | 1495704814 |
| 14 | 7596893701 |
| 15 | 38524719319 |
| 16 | 195316135549 |
| 17 | 990921152875 |
| 18 | 5025881864695 |
| 19 | 25488754160616 |
| 20 | 129285719478533 |
| 21 | 655737002374833 |
[4,36,135,620,3637,17450,86139,451210,2267574, 11420744,58323254,295406628,1495704814,7596893701, 38524719319,195316135549,990921152875, 5025881864695,25488754160616,129285719478533, 655737002374833] |