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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 104 |
| 5 | 612 |
| 6 | 3056 |
| 7 | 16368 |
| 8 | 82656 |
| 9 | 397040 |
| 10 | 1873344 |
| 11 | 8687872 |
| 12 | 39621504 |
| 13 | 178384960 |
| 14 | 794593024 |
| 15 | 3506334976 |
| 16 | 15347019264 |
| 17 | 66696520448 |
| 18 | 288032791552 |
| 19 | 1236901206016 |
| 20 | 5284853921792 |
| 21 | 22477522539520 |
| 22 | 95205886291968 |
[0,0,4,104,612,3056,16368,82656,397040,1873344, 8687872,39621504,178384960,794593024,3506334976, 15347019264,66696520448,288032791552, 1236901206016,5284853921792,22477522539520, 95205886291968] |