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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 36 |
| 4 | 108 |
| 5 | 324 |
| 6 | 948 |
| 7 | 2796 |
| 8 | 8196 |
| 9 | 24060 |
| 10 | 70188 |
| 11 | 205284 |
| 12 | 597996 |
| 13 | 1744548 |
| 14 | 5073900 |
| 15 | 14774652 |
| 16 | 42922452 |
| 17 | 124814484 |
| 18 | 362267652 |
| 19 | 1052271732 |
| 20 | 3051900516 |
| 21 | 8857050204 |
| 22 | 25671988020 |
| 23 | 74449697484 |
| 24 | 215677847460 |
| 25 | 625096195404 |
| 26 | 1810062340812 |
| 27 | 5243388472212 |
[1,4,12,36,108,324,948,2796,8196,24060,70188, 205284,597996,1744548,5073900,14774652,42922452, 124814484,362267652,1052271732,3051900516, 8857050204,25671988020,74449697484,215677847460, 625096195404,1810062340812,5243388472212] |