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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 26 |
| 3 | 148 |
| 4 | 843 |
| 5 | 4632 |
| 6 | 25124 |
| 7 | 133784 |
| 8 | 703553 |
| 9 | 3655340 |
| 10 | 18800886 |
| 11 | 95819580 |
| 12 | 484416675 |
| 13 | 2431094352 |
| 14 | 12120072472 |
| 15 | 60058765072 |
| 16 | 295959923287 |
| 17 | 1450980481036 |
| 18 | 7079894939166 |
| 19 | 34393241899772 |
| 20 | 166390593502701 |
| 21 | 801877654792696 |
| 22 | 3850469199935412 |
| 23 | 18426281811165880 |
[1,4,26,148,843,4632,25124,133784,703553,3655340, 18800886,95819580,484416675,2431094352, 12120072472,60058765072,295959923287, 1450980481036,7079894939166,34393241899772, 166390593502701,801877654792696,3850469199935412, 18426281811165880] |