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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 0 |
| 3 | 2 |
| 4 | 14 |
| 5 | 54 |
| 6 | 304 |
| 7 | 2260 |
| 8 | 18108 |
| 9 | 161756 |
| 10 | 1618496 |
| 11 | 17815896 |
| 12 | 213767080 |
| 13 | 2778833992 |
| 14 | 38904145344 |
| 15 | 583563781424 |
| 16 | 9337011390224 |
| 17 | 158729175524880 |
| 18 | 2857125341582848 |
| 19 | 54285381652008736 |
| 20 | 1085707629235539936 |
| 21 | 22799860214350346336 |
| 22 | 501596924799005576960 |
[1,1,0,2,14,54,304,2260,18108,161756,1618496, 17815896,213767080,2778833992,38904145344, 583563781424,9337011390224,158729175524880, 2857125341582848,54285381652008736, 1085707629235539936,22799860214350346336, 501596924799005576960] |