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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 16 |
| 3 | 54 |
| 4 | 176 |
| 5 | 564 |
| 6 | 1790 |
| 7 | 5646 |
| 8 | 17732 |
| 9 | 55512 |
| 10 | 173354 |
| 11 | 540258 |
| 12 | 1680848 |
| 13 | 5221740 |
| 14 | 16200758 |
| 15 | 50204790 |
| 16 | 155413724 |
| 17 | 480622848 |
| 18 | 1484980802 |
| 19 | 4584213642 |
| 20 | 14140323560 |
| 21 | 43583756436 |
| 22 | 134239102286 |
| 23 | 413179757214 |
| 24 | 1270924525556 |
| 25 | 3906925144104 |
[4,16,54,176,564,1790,5646,17732,55512,173354, 540258,1680848,5221740,16200758,50204790, 155413724,480622848,1484980802,4584213642, 14140323560,43583756436,134239102286,413179757214, 1270924525556,3906925144104] |