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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 21 |
| 3 | 108 |
| 4 | 548 |
| 5 | 3102 |
| 6 | 17101 |
| 7 | 95674 |
| 8 | 543837 |
| 9 | 3094889 |
| 10 | 17654882 |
| 11 | 100922299 |
| 12 | 576885277 |
| 13 | 3298560872 |
| 14 | 18868606128 |
| 15 | 107935859047 |
| 16 | 617459322870 |
| 17 | 3532519181939 |
| 18 | 20210076149240 |
| 19 | 115625671366613 |
| 20 | 661524633792529 |
[4,21,108,548,3102,17101,95674,543837,3094889, 17654882,100922299,576885277,3298560872, 18868606128,107935859047,617459322870, 3532519181939,20210076149240,115625671366613, 661524633792529] |