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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 12 |
| 3 | 41 |
| 4 | 159 |
| 5 | 684 |
| 6 | 3204 |
| 7 | 16042 |
| 8 | 84412 |
| 9 | 460174 |
| 10 | 2570411 |
| 11 | 14593499 |
| 12 | 83749169 |
| 13 | 484000704 |
| 14 | 2809880001 |
| 15 | 16360962717 |
| 16 | 95445840289 |
| 17 | 557493277222 |
| 18 | 3258874744858 |
| 19 | 19059827706050 |
| 20 | 111510210083018 |
| 21 | 652534784892188 |
| 22 | 3819030330465099 |
[4,12,41,159,684,3204,16042,84412,460174,2570411, 14593499,83749169,484000704,2809880001, 16360962717,95445840289,557493277222, 3258874744858,19059827706050,111510210083018, 652534784892188,3819030330465099] |