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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 8 |
| 5 | 20 |
| 6 | 40 |
| 7 | 70 |
| 8 | 9072 |
| 9 | 80808 |
| 10 | 470640 |
| 11 | 2217930 |
| 12 | 91956920 |
| 13 | 1649007932 |
| 14 | 18956858648 |
| 15 | 169921752910 |
| 16 | 4310715370080 |
| 17 | 111302746115920 |
| 18 | 2053356893604192 |
| 19 | 29525879498171538 |
| 20 | 660295352236840680 |
| 21 | 19735183465373056100 |
| 22 | 504257138580203577800 |
[1,0,0,0,8,20,40,70,9072,80808,470640,2217930, 91956920,1649007932,18956858648,169921752910, 4310715370080,111302746115920,2053356893604192, 29525879498171538,660295352236840680, 19735183465373056100,504257138580203577800] |