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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 16 |
| 5 | 78 |
| 6 | 457 |
| 7 | 2938 |
| 8 | 20118 |
| 9 | 144113 |
| 10 | 1065328 |
| 11 | 8068332 |
| 12 | 62297808 |
| 13 | 488755938 |
| 14 | 3886672165 |
| 15 | 31269417102 |
| 16 | 254141551498 |
| 17 | 2084129777764 |
| 18 | 17228043363781 |
| 19 | 143432427097935 |
| 20 | 1201853492038096 |
| 21 | 10129428318995227 |
| 22 | 85826173629557200 |
[1,1,1,4,16,78,457,2938,20118,144113,1065328, 8068332,62297808,488755938,3886672165,31269417102, 254141551498,2084129777764,17228043363781, 143432427097935,1201853492038096, 10129428318995227,85826173629557200] |