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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 720 |
| 7 | 15120 |
| 8 | 191520 |
| 9 | 1905120 |
| 10 | 16435440 |
| 11 | 129230640 |
| 12 | 953029440 |
| 13 | 6711344640 |
| 14 | 45674188560 |
| 15 | 302899156560 |
| 16 | 1969147121760 |
| 17 | 12604139926560 |
| 18 | 79694820748080 |
| 19 | 499018753280880 |
| 20 | 3100376804676480 |
| 21 | 19141689213218880 |
| 22 | 117579844328562000 |
[0,0,0,0,0,720,15120,191520,1905120,16435440, 129230640,953029440,6711344640,45674188560, 302899156560,1969147121760,12604139926560, 79694820748080,499018753280880,3100376804676480, 19141689213218880,117579844328562000] |