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| n | a(n) |
|---|---|
| 4 | 0 |
| 5 | 0 |
| 6 | 1 |
| 7 | 2 |
| 8 | 3 |
| 9 | 7 |
| 10 | 22 |
| 11 | 57 |
| 12 | 174 |
| 13 | 554 |
| 14 | 1848 |
| 15 | 6291 |
| 16 | 22052 |
| 17 | 78361 |
| 18 | 282420 |
[0,0,1,2,3,7,22,57,174,554,1848,6291,22052,78361, 282420] |