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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 4 |
| 6 | 15 |
| 7 | 56 |
| 8 | 214 |
| 9 | 854 |
| 10 | 3607 |
| 11 | 16172 |
| 12 | 76853 |
| 13 | 386082 |
| 14 | 2044198 |
| 15 | 11373124 |
| 16 | 66300473 |
| 17 | 403939612 |
| 18 | 2566116299 |
| 19 | 16962629860 |
| 20 | 116452790838 |
| 21 | 828903740138 |
| 22 | 6107712000563 |
| 23 | 46521422681724 |
| 24 | 365811331693305 |
| 25 | 2965957618809246 |
| 26 | 24767913121016790 |
| 27 | 212803409969904264 |
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