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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 8 |
| 3 | 40 |
| 4 | 221 |
| 5 | 1288 |
| 6 | 7752 |
| 7 | 47652 |
| 8 | 297275 |
| 9 | 1874730 |
| 10 | 11920740 |
| 11 | 76292736 |
| 12 | 490828828 |
| 13 | 3171317360 |
| 14 | 20563942288 |
| 15 | 133749903324 |
| 16 | 872196460359 |
| 17 | 5700580759510 |
| 18 | 37332393806400 |
| 19 | 244914161562840 |
| 20 | 1609234420792845 |
[1,2,8,40,221,1288,7752,47652,297275,1874730, 11920740,76292736,490828828,3171317360, 20563942288,133749903324,872196460359, 5700580759510,37332393806400,244914161562840, 1609234420792845] |