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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 40 |
| 4 | 118 |
| 5 | 358 |
| 6 | 936 |
| 7 | 2600 |
| 8 | 6212 |
| 9 | 16068 |
| 10 | 34936 |
| 11 | 83708 |
| 12 | 163452 |
| 13 | 357056 |
| 14 | 613592 |
| 15 | 1205716 |
| 16 | 1770616 |
| 17 | 3073480 |
| 18 | 3715920 |
| 19 | 5573480 |
| 20 | 5255048 |
| 21 | 6591160 |
| 22 | 4353912 |
| 23 | 4330096 |
| 24 | 1513712 |
| 25 | 1061392 |
| 26 | 0 |
[1,4,12,40,118,358,936,2600,6212,16068,34936, 83708,163452,357056,613592,1205716,1770616, 3073480,3715920,5573480,5255048,6591160,4353912, 4330096,1513712,1061392,0] |