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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 3 |
| 4 | 12 |
| 5 | 80 |
| 6 | 750 |
| 7 | 9072 |
| 8 | 134456 |
| 9 | 2359296 |
| 10 | 47829690 |
| 11 | 1100000000 |
| 12 | 28295372292 |
| 13 | 804925734912 |
| 14 | 25090245516518 |
| 15 | 850408685629440 |
| 16 | 31139121093750000 |
| 17 | 1224979098644774912 |
| 18 | 51523614927176684274 |
| 19 | 2307351090835290783744 |
| 20 | 109607737155696043718780 |
| 21 | 5505024000000000000000000 |
[1,3,12,80,750,9072,134456,2359296,47829690, 1100000000,28295372292,804925734912, 25090245516518,850408685629440,31139121093750000, 1224979098644774912,51523614927176684274, 2307351090835290783744,109607737155696043718780, 5505024000000000000000000] |