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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 1 |
| 4 | 1 |
| 5 | 7 |
| 6 | 20 |
| 7 | 49 |
| 8 | 175 |
| 9 | 323 |
| 10 | 1085 |
| 11 | 2290 |
| 12 | 6489 |
| 13 | 15751 |
| 14 | 41749 |
| 15 | 105514 |
| 16 | 276079 |
| 17 | 706396 |
| 18 | 1825615 |
| 19 | 4714184 |
| 20 | 12103729 |
| 21 | 31297188 |
| 22 | 80431077 |
| 23 | 207561706 |
| 24 | 534335127 |
| 25 | 1377615603 |
| 26 | 3548250067 |
| 27 | 9145959294 |
| 28 | 23561913471 |
| 29 | 60719538527 |
| 30 | 156456169973 |
[1,0,1,1,7,20,49,175,323,1085,2290,6489,15751, 41749,105514,276079,706396,1825615,4714184, 12103729,31297188,80431077,207561706,534335127, 1377615603,3548250067,9145959294,23561913471, 60719538527,156456169973] |