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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 4 |
| 3 | 56 |
| 4 | 560 |
| 5 | 4960 |
| 6 | 41664 |
| 7 | 341376 |
| 8 | 2763520 |
| 9 | 22238720 |
| 10 | 178433024 |
| 11 | 1429559296 |
| 12 | 11444858880 |
| 13 | 91592417280 |
| 14 | 732873539584 |
| 15 | 5863525154816 |
| 16 | 46910348656640 |
| 17 | 375291379056640 |
| 18 | 3002365391929344 |
| 19 | 24019060573863936 |
| 20 | 192153034345676800 |
| 21 | 1537226473786572800 |
[0,0,4,56,560,4960,41664,341376,2763520,22238720, 178433024,1429559296,11444858880,91592417280, 732873539584,5863525154816,46910348656640, 375291379056640,3002365391929344, 24019060573863936,192153034345676800, 1537226473786572800] |