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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 25 |
| 3 | 136 |
| 4 | 664 |
| 5 | 2824 |
| 6 | 11668 |
| 7 | 47364 |
| 8 | 191084 |
| 9 | 768413 |
| 10 | 3084521 |
| 11 | 12382973 |
| 12 | 49700585 |
| 13 | 199608265 |
| 14 | 801170741 |
| 15 | 3207852473 |
[1,4,25,136,664,2824,11668,47364,191084,768413, 3084521,12382973,49700585,199608265,801170741, 3207852473] |