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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 6 |
| 3 | 28 |
| 4 | 54 |
| 5 | 405 |
| 6 | 486 |
| 7 | 2808 |
| 8 | 4860 |
| 9 | 21870 |
| 10 | 40824 |
| 11 | 192456 |
| 12 | 524160 |
| 13 | 708588 |
| 14 | 4059072 |
| 15 | 14348907 |
| 16 | 58576608 |
| 17 | 123731712 |
| 18 | 462944160 |
| 19 | 1837080000 |
| 20 | 3874204890 |
| 21 | 11809800000 |
| 22 | 48183984000 |
| 23 | 65086642152 |
| 24 | 339033848832 |
| 25 | 1360965131136 |
| 26 | 2928898896840 |
| 27 | 6595446404736 |
[2,6,28,54,405,486,2808,4860,21870,40824,192456, 524160,708588,4059072,14348907,58576608,123731712, 462944160,1837080000,3874204890,11809800000, 48183984000,65086642152,339033848832, 1360965131136,2928898896840,6595446404736] |