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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 10 |
| 6 | 0 |
| 7 | 8 |
| 8 | 24 |
| 9 | 72 |
| 10 | 116 |
| 11 | 384 |
| 12 | 1660 |
| 13 | 7344 |
| 14 | 24364 |
| 15 | 130408 |
| 16 | 743360 |
| 17 | 4242704 |
| 18 | 27018788 |
| 19 | 190618152 |
| 20 | 1431986780 |
| 21 | 11053915716 |
[1,0,0,2,10,0,8,24,72,116,384,1660,7344,24364, 130408,743360,4242704,27018788,190618152, 1431986780,11053915716] |