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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 24 |
| 4 | 100 |
| 5 | 420 |
| 6 | 1792 |
| 7 | 7752 |
| 8 | 33858 |
| 9 | 148940 |
| 10 | 658944 |
| 11 | 2929056 |
| 12 | 13070876 |
| 13 | 58521344 |
| 14 | 262754040 |
| 15 | 1182619280 |
| 16 | 5334172518 |
| 17 | 24104916504 |
| 18 | 109111142376 |
| 19 | 494630028200 |
| 20 | 2245300152480 |
| 21 | 10204575481320 |
| 22 | 46429481139000 |
| 23 | 211460450151600 |
| 24 | 963971663881200 |
| 25 | 4398118872144192 |
[1,2,6,24,100,420,1792,7752,33858,148940,658944, 2929056,13070876,58521344,262754040,1182619280, 5334172518,24104916504,109111142376,494630028200, 2245300152480,10204575481320,46429481139000, 211460450151600,963971663881200,4398118872144192] |