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| n | a(n) |
|---|---|
| 1 | 6 |
| 2 | 24 |
| 3 | 132 |
| 4 | 804 |
| 5 | 5196 |
| 6 | 34872 |
| 7 | 240288 |
| 8 | 1688244 |
| 9 | 12040188 |
| 10 | 86892384 |
| 11 | 633162360 |
| 12 | 4650680640 |
| 13 | 34390540320 |
| 14 | 255773538240 |
| 15 | 1911730760832 |
| 16 | 14350853162676 |
| 17 | 108139250403804 |
| 18 | 817629606524112 |
| 19 | 6200696697358344 |
| 20 | 47152195812692664 |
[6,24,132,804,5196,34872,240288,1688244,12040188, 86892384,633162360,4650680640,34390540320, 255773538240,1911730760832,14350853162676, 108139250403804,817629606524112,6200696697358344, 47152195812692664] |