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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 6 |
| 5 | 18 |
| 6 | 42 |
| 7 | 98 |
| 8 | 210 |
| 9 | 450 |
| 10 | 930 |
| 11 | 1922 |
| 12 | 3906 |
| 13 | 7938 |
| 14 | 16002 |
| 15 | 32258 |
| 16 | 64770 |
| 17 | 130050 |
| 18 | 260610 |
| 19 | 522242 |
| 20 | 1045506 |
| 21 | 2093058 |
| 22 | 4188162 |
| 23 | 8380418 |
| 24 | 16764930 |
| 25 | 33538050 |
| 26 | 67084290 |
| 27 | 134184962 |
| 28 | 268386306 |
| 29 | 536805378 |
| 30 | 1073643522 |
[0,0,0,2,6,18,42,98,210,450,930,1922,3906,7938, 16002,32258,64770,130050,260610,522242,1045506, 2093058,4188162,8380418,16764930,33538050, 67084290,134184962,268386306,536805378,1073643522] |