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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 121 |
| 6 | 732 |
| 7 | 5166 |
| 8 | 41664 |
| 9 | 378001 |
| 10 | 3810512 |
| 11 | 42253926 |
| 12 | 511139904 |
| 13 | 6698457481 |
| 14 | 94535404992 |
| 15 | 1429477706286 |
| 16 | 23056267551744 |
| 17 | 395120495014561 |
| 18 | 7169579673404672 |
| 19 | 137321623511274246 |
| 20 | 2768602189953629184 |
| 21 | 58609968225266985241 |
| 22 | 1299827736206335767552 |
| 23 | 30137364376923272989806 |
[1,1,2,6,24,121,732,5166,41664,378001,3810512, 42253926,511139904,6698457481,94535404992, 1429477706286,23056267551744,395120495014561, 7169579673404672,137321623511274246, 2768602189953629184,58609968225266985241, 1299827736206335767552,30137364376923272989806] |