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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 5 |
| 3 | 20 |
| 4 | 90 |
| 5 | 440 |
| 6 | 2236 |
| 7 | 11720 |
| 8 | 62960 |
| 9 | 344690 |
| 10 | 1916170 |
| 11 | 10787762 |
| 12 | 61380770 |
| 13 | 352410760 |
| 14 | 2039099640 |
| 15 | 11878519460 |
| 16 | 69608606348 |
| 17 | 410056995475 |
| 18 | 2426936098575 |
| 19 | 14424334077975 |
| 20 | 86055337016695 |
| 21 | 515170271387970 |
| 22 | 3093724519080210 |
| 23 | 18631778892165080 |
[1,1,5,20,90,440,2236,11720,62960,344690,1916170, 10787762,61380770,352410760,2039099640, 11878519460,69608606348,410056995475, 2426936098575,14424334077975,86055337016695, 515170271387970,3093724519080210, 18631778892165080] |