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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 4 |
| 4 | 10 |
| 5 | 18 |
| 6 | 38 |
| 7 | 68 |
| 8 | 138 |
| 9 | 250 |
| 10 | 502 |
| 11 | 922 |
| 12 | 1846 |
| 13 | 3430 |
| 14 | 6862 |
| 15 | 12868 |
| 16 | 25738 |
| 17 | 48618 |
| 18 | 97238 |
| 19 | 184754 |
| 20 | 369510 |
| 21 | 705430 |
| 22 | 1410862 |
| 23 | 2704154 |
| 24 | 5408310 |
| 25 | 10400598 |
| 26 | 20801198 |
| 27 | 40116598 |
| 28 | 80233198 |
| 29 | 155117518 |
| 30 | 310235038 |
[0,0,2,4,10,18,38,68,138,250,502,922,1846,3430, 6862,12868,25738,48618,97238,184754,369510,705430, 1410862,2704154,5408310,10400598,20801198, 40116598,80233198,155117518,310235038] |