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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 120 |
| 5 | 1680 |
| 6 | 30120 |
| 7 | 658560 |
| 8 | 16994880 |
| 9 | 505612800 |
| 10 | 17037851040 |
| 11 | 641393786880 |
| 12 | 26678131159680 |
| 13 | 1215016298496000 |
| 14 | 60135628841608320 |
| 15 | 3213908573331456000 |
| 16 | 184463573184501811200 |
| 17 | 11316253482729190195200 |
| 18 | 738934748606732911833600 |
| 19 | 51171600229826941786521600 |
[1,2,12,120,1680,30120,658560,16994880,505612800, 17037851040,641393786880,26678131159680, 1215016298496000,60135628841608320, 3213908573331456000,184463573184501811200, 11316253482729190195200,738934748606732911833600, 51171600229826941786521600] |