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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 5 |
| 3 | 23 |
| 4 | 120 |
| 5 | 724 |
| 6 | 5012 |
| 7 | 39332 |
| 8 | 345832 |
| 9 | 3371976 |
| 10 | 36135792 |
| 11 | 422379792 |
| 12 | 5349561984 |
| 13 | 72996193152 |
| 14 | 1067779243008 |
| 15 | 16670798231040 |
| 16 | 276718772067840 |
| 17 | 4866610479828480 |
| 18 | 90401487246167040 |
| 19 | 1768784607499944960 |
| 20 | 36360467544043008000 |
| 21 | 783508616506603008000 |
[1,5,23,120,724,5012,39332,345832,3371976, 36135792,422379792,5349561984,72996193152, 1067779243008,16670798231040,276718772067840, 4866610479828480,90401487246167040, 1768784607499944960,36360467544043008000, 783508616506603008000] |