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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 10 |
| 6 | 4 |
| 7 | 40 |
| 8 | 92 |
| 9 | 352 |
| 10 | 724 |
| 11 | 2680 |
| 12 | 14200 |
| 13 | 73712 |
| 14 | 365596 |
| 15 | 2279184 |
| 16 | 14772512 |
| 17 | 95815104 |
| 18 | 666090624 |
| 19 | 4968057848 |
| 20 | 39029188884 |
| 21 | 314666222712 |
| 22 | 2691008701644 |
| 23 | 24233937684440 |
| 24 | 227514171973736 |
| 25 | 2207893435808352 |
| 26 | 22317699616364044 |
| 27 | 234907967154122528 |
[1,1,0,0,2,10,4,40,92,352,724,2680,14200,73712, 365596,2279184,14772512,95815104,666090624, 4968057848,39029188884,314666222712,2691008701644, 24233937684440,227514171973736,2207893435808352, 22317699616364044,234907967154122528] |