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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 20 |
| 3 | 104 |
| 4 | 336 |
| 5 | 1696 |
| 6 | 5440 |
| 7 | 27264 |
| 8 | 87296 |
| 9 | 436736 |
| 10 | 1397760 |
| 11 | 6989824 |
| 12 | 22368256 |
| 13 | 111845376 |
| 14 | 357908480 |
| 15 | 1789558784 |
| 16 | 5726601216 |
| 17 | 28633071616 |
| 18 | 91625881600 |
| 19 | 458129670144 |
| 20 | 1466015154176 |
| 21 | 7330076819456 |
| 22 | 23456246661120 |
| 23 | 117281237499904 |
| 24 | 375299963355136 |
[1,6,20,104,336,1696,5440,27264,87296,436736, 1397760,6989824,22368256,111845376,357908480, 1789558784,5726601216,28633071616,91625881600, 458129670144,1466015154176,7330076819456, 23456246661120,117281237499904,375299963355136] |