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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 22 |
| 5 | 96 |
| 6 | 492 |
| 7 | 2952 |
| 8 | 20588 |
| 9 | 164990 |
| 10 | 1497740 |
| 11 | 15187692 |
| 12 | 169974040 |
| 13 | 2078905752 |
| 14 | 27567259896 |
| 15 | 393759207372 |
| 16 | 6025346314756 |
| 17 | 98317949671110 |
| 18 | 1703879074519500 |
| 19 | 31251488731748108 |
| 20 | 604748393942784976 |
| 21 | 12312387380060084768 |
| 22 | 263079571362773145632 |
[1,1,2,6,22,96,492,2952,20588,164990,1497740, 15187692,169974040,2078905752,27567259896, 393759207372,6025346314756,98317949671110, 1703879074519500,31251488731748108, 604748393942784976,12312387380060084768, 263079571362773145632] |