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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 4 |
| 5 | 14 |
| 6 | 104 |
| 7 | 594 |
| 8 | 3988 |
| 9 | 29188 |
| 10 | 227588 |
| 11 | 1983482 |
| 12 | 18398780 |
| 13 | 188210020 |
| 14 | 2030025592 |
| 15 | 23828759942 |
| 16 | 293948660282 |
| 17 | 3909402733418 |
[0,0,0,4,14,104,594,3988,29188,227588,1983482, 18398780,188210020,2030025592,23828759942, 293948660282,3909402733418] |