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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 20 |
| 3 | 45 |
| 4 | 320 |
| 5 | 6615 |
| 6 | 382200 |
| 7 | 680890228200 |
| 8 | 8169778639360 |
| 9 | 27445575588992 |
| 10 | 56626123593600 |
| 11 | 1235050901504640 |
[1,20,45,320,6615,382200,680890228200, 8169778639360,27445575588992,56626123593600, 1235050901504640] |