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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 8 |
| 4 | 28 |
| 5 | 88 |
| 6 | 270 |
| 7 | 816 |
| 8 | 2456 |
| 9 | 7376 |
| 10 | 22138 |
| 11 | 66424 |
| 12 | 199284 |
| 13 | 597864 |
| 14 | 1793606 |
| 15 | 5380832 |
| 16 | 16142512 |
| 17 | 48427552 |
| 18 | 145282674 |
| 19 | 435848040 |
| 20 | 1307544140 |
| 21 | 3922632440 |
| 22 | 11767897342 |
| 23 | 35303692048 |
| 24 | 105911076168 |
| 25 | 317733228528 |
[0,2,8,28,88,270,816,2456,7376,22138,66424,199284, 597864,1793606,5380832,16142512,48427552, 145282674,435848040,1307544140,3922632440, 11767897342,35303692048,105911076168,317733228528] |