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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 720 |
| 7 | 1560 |
| 8 | 2352 |
| 9 | 4704 |
| 10 | 10946 |
| 11 | 28655 |
| 12 | 83622 |
| 13 | 230716 |
| 14 | 604056 |
| 15 | 1498904 |
| 16 | 3627824 |
| 17 | 8885872 |
| 18 | 22445448 |
| 19 | 57373588 |
| 20 | 147086040 |
| 21 | 375553984 |
| 22 | 951141040 |
| 23 | 2395384168 |
| 24 | 6035991620 |
| 25 | 15241258584 |
| 26 | 38573288432 |
| 27 | 97763641880 |
| 28 | 247758889696 |
[1,2,6,24,120,720,1560,2352,4704,10946,28655, 83622,230716,604056,1498904,3627824,8885872, 22445448,57373588,147086040,375553984,951141040, 2395384168,6035991620,15241258584,38573288432, 97763641880,247758889696] |