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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 54 |
| 4 | 594 |
| 5 | 7371 |
| 6 | 99144 |
| 7 | 1412802 |
| 8 | 21025818 |
| 9 | 323686935 |
| 10 | 5120138790 |
| 11 | 82812679560 |
| 12 | 1364498150904 |
| 13 | 22839100002036 |
| 14 | 387477144862128 |
| 15 | 6651170184185802 |
| 16 | 115346229450879978 |
| 17 | 2018559015390399615 |
| 18 | 35610482089433479410 |
| 19 | 632770874050702595670 |
| 20 | 11317118106279639106530 |
[1,1,6,54,594,7371,99144,1412802,21025818, 323686935,5120138790,82812679560,1364498150904, 22839100002036,387477144862128,6651170184185802, 115346229450879978,2018559015390399615, 35610482089433479410,632770874050702595670, 11317118106279639106530] |