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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 2 |
| 4 | 7 |
| 5 | 20 |
| 6 | 60 |
| 7 | 176 |
| 8 | 517 |
| 9 | 1512 |
| 10 | 4415 |
| 11 | 12870 |
| 12 | 37477 |
| 13 | 109044 |
| 14 | 317109 |
| 15 | 921870 |
| 16 | 2679510 |
| 17 | 7787904 |
| 18 | 22636503 |
| 19 | 65804638 |
| 20 | 191332945 |
| 21 | 556456060 |
| 22 | 1618813834 |
| 23 | 4710869108 |
| 24 | 13713658368 |
| 25 | 39935698400 |
| 26 | 116340344575 |
| 27 | 339050396646 |
| 28 | 988474306017 |
[1,2,7,20,60,176,517,1512,4415,12870,37477,109044, 317109,921870,2679510,7787904,22636503,65804638, 191332945,556456060,1618813834,4710869108, 13713658368,39935698400,116340344575,339050396646, 988474306017] |