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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 720 |
| 2 | 179280 |
| 3 | 16954560 |
| 4 | 396974160 |
| 5 | 4632858720 |
| 6 | 34413301440 |
| 7 | 187477879680 |
| 8 | 814940600400 |
| 9 | 2975469665040 |
| 10 | 9486467837280 |
| 11 | 27053330840640 |
| 12 | 70485969919680 |
| 13 | 169930679355360 |
| 14 | 384163875688320 |
| 15 | 820167497170560 |
| 16 | 1668890801059920 |
| 17 | 3249626139960480 |
| 18 | 6096884624994960 |
[1,720,179280,16954560,396974160,4632858720, 34413301440,187477879680,814940600400, 2975469665040,9486467837280,27053330840640, 70485969919680,169930679355360,384163875688320, 820167497170560,1668890801059920,3249626139960480, 6096884624994960] |