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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 8 |
| 5 | 54 |
| 6 | 140 |
| 7 | 1116 |
| 8 | 2976 |
| 9 | 19828 |
| 10 | 58388 |
| 11 | 443892 |
| 12 | 1036180 |
| 13 | 9390024 |
| 14 | 27996724 |
| 15 | 175396812 |
[0,0,4,8,54,140,1116,2976,19828,58388,443892, 1036180,9390024,27996724,175396812] |