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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 18 |
| 4 | 96 |
| 5 | 960 |
| 6 | 11520 |
| 7 | 161280 |
| 8 | 2580480 |
| 9 | 46448640 |
| 10 | 928972800 |
| 11 | 20437401600 |
| 12 | 490497638400 |
| 13 | 12752938598400 |
| 14 | 357082280755200 |
| 15 | 10712468422656000 |
| 16 | 342798989524992000 |
| 17 | 11655165643849728000 |
| 18 | 419585963178590208000 |
[0,0,2,18,96,960,11520,161280,2580480,46448640, 928972800,20437401600,490497638400,12752938598400, 357082280755200,10712468422656000, 342798989524992000,11655165643849728000, 419585963178590208000] |