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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 11 |
| 4 | 40 |
| 5 | 169 |
| 6 | 838 |
| 7 | 4769 |
| 8 | 30552 |
| 9 | 217609 |
| 10 | 1707386 |
| 11 | 14606605 |
| 12 | 135377180 |
| 13 | 1350221253 |
| 14 | 14418478134 |
| 15 | 164081870257 |
| 16 | 1981956038800 |
| 17 | 25322934226033 |
| 18 | 341140167526450 |
| 19 | 4832627675466965 |
| 20 | 71801774865134884 |
[1,2,4,11,40,169,838,4769,30552,217609,1707386, 14606605,135377180,1350221253,14418478134, 164081870257,1981956038800,25322934226033, 341140167526450,4832627675466965, 71801774865134884] |