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| n | a(n) |
|---|---|
| 4 | 1 |
| 5 | 4 |
| 6 | 20 |
| 7 | 100 |
| 8 | 525 |
| 9 | 2912 |
| 10 | 17052 |
| 11 | 105240 |
| 12 | 683100 |
| 13 | 4652340 |
| 14 | 33168850 |
| 15 | 246999480 |
| 16 | 1917186635 |
| 17 | 15480884720 |
| 18 | 129811538960 |
| 19 | 1128494172720 |
| 20 | 10155257740443 |
| 21 | 94465951576560 |
| 22 | 907162152191470 |
| 23 | 8982422995787780 |
| 24 | 91603484234843812 |
[1,4,20,100,525,2912,17052,105240,683100,4652340, 33168850,246999480,1917186635,15480884720, 129811538960,1128494172720,10155257740443, 94465951576560,907162152191470,8982422995787780, 91603484234843812] |