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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 6 |
| 6 | 20 |
| 7 | 48 |
| 8 | 288 |
| 9 | 1344 |
| 10 | 6624 |
| 11 | 28512 |
| 12 | 212544 |
| 13 | 1425600 |
| 14 | 10056960 |
| 15 | 61378560 |
| 16 | 600514560 |
| 17 | 5185658880 |
| 18 | 46664294400 |
| 19 | 374492160000 |
| 20 | 4406814720000 |
| 21 | 46820229120000 |
| 22 | 515545067520000 |
| 23 | 5128069201920000 |
| 24 | 70905056624640000 |
| 25 | 893661057515520000 |
| 26 | 11621453908377600000 |
[1,1,1,2,6,20,48,288,1344,6624,28512,212544, 1425600,10056960,61378560,600514560,5185658880, 46664294400,374492160000,4406814720000, 46820229120000,515545067520000,5128069201920000, 70905056624640000,893661057515520000, 11621453908377600000] |