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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 18 |
| 4 | 85 |
| 5 | 411 |
| 6 | 2013 |
| 7 | 9933 |
| 8 | 49236 |
| 9 | 244750 |
| 10 | 1218888 |
| 11 | 6077644 |
| 12 | 30329434 |
| 13 | 151439158 |
| 14 | 756452890 |
| 15 | 3779590010 |
| 16 | 18888255205 |
| 17 | 94405918355 |
| 18 | 471899946985 |
| 19 | 2359022096225 |
| 20 | 11793343217935 |
| 21 | 58960151969255 |
| 22 | 294776293579255 |
[1,4,18,85,411,2013,9933,49236,244750,1218888, 6077644,30329434,151439158,756452890,3779590010, 18888255205,94405918355,471899946985, 2359022096225,11793343217935,58960151969255, 294776293579255] |