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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 119 |
| 6 | 709 |
| 7 | 4928 |
| 8 | 39144 |
| 9 | 349776 |
| 10 | 3472811 |
| 11 | 37928331 |
| 12 | 451891992 |
| 13 | 5832672456 |
| 14 | 81074690424 |
| 15 | 1207441809209 |
| 16 | 19181203110129 |
| 17 | 323753459184738 |
| 18 | 5785975294622694 |
| 19 | 109149016813544376 |
| 20 | 2167402030585724571 |
| 21 | 45190632809497874161 |
| 22 | 987099099863360190632 |
[1,1,2,6,24,119,709,4928,39144,349776,3472811, 37928331,451891992,5832672456,81074690424, 1207441809209,19181203110129,323753459184738, 5785975294622694,109149016813544376, 2167402030585724571,45190632809497874161, 987099099863360190632] |