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| n | a(n) |
|---|---|
| 4 | 1 |
| 5 | 8 |
| 6 | 40 |
| 7 | 168 |
| 8 | 676 |
| 9 | 2672 |
| 10 | 10376 |
| 11 | 39824 |
| 12 | 151878 |
| 13 | 576656 |
| 14 | 2181496 |
| 15 | 8229160 |
| 16 | 30974700 |
| 17 | 116385088 |
| 18 | 436678520 |
| 19 | 1636472360 |
| 20 | 6126647748 |
[1,8,40,168,676,2672,10376,39824,151878,576656, 2181496,8229160,30974700,116385088,436678520, 1636472360,6126647748] |