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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 68 |
| 5 | 232 |
| 6 | 792 |
| 7 | 2704 |
| 8 | 9232 |
| 9 | 31520 |
| 10 | 107616 |
| 11 | 367424 |
| 12 | 1254464 |
| 13 | 4283008 |
| 14 | 14623104 |
| 15 | 49926400 |
| 16 | 170459392 |
| 17 | 581984768 |
| 18 | 1987020288 |
| 19 | 6784111616 |
| 20 | 23162405888 |
| 21 | 79081400320 |
| 22 | 270000789504 |
| 23 | 921840357376 |
| 24 | 3147359850496 |
[1,2,6,20,68,232,792,2704,9232,31520,107616, 367424,1254464,4283008,14623104,49926400, 170459392,581984768,1987020288,6784111616, 23162405888,79081400320,270000789504,921840357376, 3147359850496] |