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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 32 |
| 4 | 90 |
| 5 | 312 |
| 6 | 1288 |
| 7 | 5504 |
| 8 | 22608 |
| 9 | 88660 |
| 10 | 339064 |
| 11 | 1297056 |
| 12 | 5043376 |
| 13 | 19975256 |
| 14 | 80027280 |
| 15 | 321692928 |
| 16 | 1291650786 |
| 17 | 5177295432 |
| 18 | 20748447108 |
| 19 | 83279292960 |
| 20 | 335056780464 |
| 21 | 1351064867328 |
| 22 | 5456890474248 |
| 23 | 22063059606912 |
[1,4,12,32,90,312,1288,5504,22608,88660,339064, 1297056,5043376,19975256,80027280,321692928, 1291650786,5177295432,20748447108,83279292960, 335056780464,1351064867328,5456890474248, 22063059606912] |