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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 17 |
| 3 | 73 |
| 4 | 311 |
| 5 | 1309 |
| 6 | 5447 |
| 7 | 22453 |
| 8 | 91871 |
| 9 | 373789 |
| 10 | 1514327 |
| 11 | 6115333 |
| 12 | 24636431 |
| 13 | 99073069 |
| 14 | 397878407 |
| 15 | 1596280213 |
| 16 | 6399436991 |
| 17 | 25640729149 |
| 18 | 102691925687 |
| 19 | 411154861093 |
| 20 | 1645781181551 |
| 21 | 6586610462029 |
| 22 | 26356900104167 |
[1,4,17,73,311,1309,5447,22453,91871,373789, 1514327,6115333,24636431,99073069,397878407, 1596280213,6399436991,25640729149,102691925687, 411154861093,1645781181551,6586610462029, 26356900104167] |