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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 30 |
| 5 | 180 |
| 6 | 1260 |
| 7 | 10080 |
| 8 | 100800 |
| 9 | 1108800 |
| 10 | 13305600 |
| 11 | 172972800 |
| 12 | 2421619200 |
| 13 | 36324288000 |
| 14 | 617512896000 |
| 15 | 11115232128000 |
| 16 | 211189410432000 |
| 17 | 4223788208640000 |
| 18 | 88699552381440000 |
| 19 | 1951390152391680000 |
[1,2,6,30,180,1260,10080,100800,1108800,13305600, 172972800,2421619200,36324288000,617512896000, 11115232128000,211189410432000,4223788208640000, 88699552381440000,1951390152391680000] |