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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 5 |
| 4 | 23 |
| 5 | 122 |
| 6 | 754 |
| 7 | 5364 |
| 8 | 43308 |
| 9 | 391824 |
| 10 | 3929616 |
| 11 | 43287840 |
| 12 | 519711840 |
| 13 | 6755460480 |
| 14 | 94527008640 |
| 15 | 1416783432960 |
| 16 | 22646604153600 |
| 17 | 384576130713600 |
| 18 | 6914404440115200 |
| 19 | 131217341055897600 |
| 20 | 2621176954176614400 |
[0,1,5,23,122,754,5364,43308,391824,3929616, 43287840,519711840,6755460480,94527008640, 1416783432960,22646604153600,384576130713600, 6914404440115200,131217341055897600, 2621176954176614400] |