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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 2 |
| 4 | 6 |
| 5 | 24 |
| 6 | 44 |
| 7 | 136 |
| 8 | 298 |
| 9 | 914 |
| 10 | 2462 |
| 11 | 6464 |
| 12 | 17740 |
| 13 | 47840 |
| 14 | 133618 |
| 15 | 366162 |
| 16 | 1011190 |
| 17 | 2801144 |
| 18 | 7775916 |
| 19 | 21680712 |
| 20 | 60443514 |
| 21 | 168963010 |
| 22 | 472975278 |
| 23 | 1326349568 |
| 24 | 3725180524 |
| 25 | 10475012672 |
| 26 | 29494512354 |
| 27 | 83141905570 |
| 28 | 234634612198 |
| 29 | 662840458840 |
| 30 | 1874315939756 |
[1,0,2,2,6,24,44,136,298,914,2462,6464,17740, 47840,133618,366162,1011190,2801144,7775916, 21680712,60443514,168963010,472975278,1326349568, 3725180524,10475012672,29494512354,83141905570, 234634612198,662840458840,1874315939756] |