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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 68 |
| 5 | 744 |
| 6 | 7088 |
| 7 | 69176 |
| 8 | 658776 |
| 9 | 5995348 |
| 10 | 52831448 |
| 11 | 458439732 |
| 12 | 3944077760 |
| 13 | 33606901296 |
| 14 | 283630894720 |
| 15 | 2375471834288 |
| 16 | 19779055344468 |
| 17 | 163866917256420 |
| 18 | 1351464466008112 |
| 19 | 11100931884955344 |
| 20 | 90860898121739864 |
| 21 | 741378713523090200 |
| 22 | 6032337718479599100 |
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