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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 10 |
| 4 | 86 |
| 5 | 756 |
| 6 | 7092 |
| 7 | 71856 |
| 8 | 787824 |
| 9 | 9329760 |
| 10 | 118956960 |
| 11 | 1627067520 |
| 12 | 23786386560 |
| 13 | 370371536640 |
| 14 | 6122231942400 |
| 15 | 107109431654400 |
| 16 | 1977781262284800 |
| 17 | 38445562145894400 |
| 18 | 784885857270681600 |
| 19 | 16792523049093120000 |
| 20 | 375755553108633600000 |
| 21 | 8777531590107033600000 |
[0,1,10,86,756,7092,71856,787824,9329760, 118956960,1627067520,23786386560,370371536640, 6122231942400,107109431654400,1977781262284800, 38445562145894400,784885857270681600, 16792523049093120000,375755553108633600000, 8777531590107033600000] |