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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 36 |
| 4 | 108 |
| 5 | 324 |
| 6 | 972 |
| 7 | 2876 |
| 8 | 8364 |
| 9 | 24124 |
| 10 | 69116 |
| 11 | 196916 |
| 12 | 559604 |
| 13 | 1585764 |
| 14 | 4495740 |
| 15 | 12714796 |
| 16 | 35654620 |
| 17 | 99686708 |
| 18 | 278880060 |
| 19 | 781504972 |
| 20 | 2180418716 |
| 21 | 6079373324 |
| 22 | 16857930068 |
| 23 | 46773551052 |
| 24 | 129562831140 |
| 25 | 358157148332 |
[1,4,12,36,108,324,972,2876,8364,24124,69116, 196916,559604,1585764,4495740,12714796,35654620, 99686708,278880060,781504972,2180418716, 6079373324,16857930068,46773551052,129562831140, 358157148332] |