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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 26 |
| 4 | 168 |
| 5 | 1416 |
| 6 | 13897 |
| 7 | 153126 |
| 8 | 1893180 |
| 9 | 25796852 |
| 10 | 383636151 |
| 11 | 6177688914 |
| 12 | 106969864696 |
| 13 | 1980478817526 |
| 14 | 39015578535585 |
| 15 | 814416108606566 |
| 16 | 17947777613632128 |
| 17 | 416233580676722424 |
| 18 | 10129555365300697267 |
| 19 | 258028441032419619786 |
| 20 | 6864011282184757297896 |
[1,1,4,26,168,1416,13897,153126,1893180,25796852, 383636151,6177688914,106969864696,1980478817526, 39015578535585,814416108606566,17947777613632128, 416233580676722424,10129555365300697267, 258028441032419619786,6864011282184757297896] |