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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 40 |
| 4 | 1992 |
| 5 | 18666624 |
| 6 | 12813206169137152 |
| 7 | 33758171486592987164087845043830784 |
| 8 | 1435913805026242504952006868879460423834904914948818373264705576411070464 |
[1,2,6,40,1992,18666624,12813206169137152, 33758171486592987164087845043830784, 14359138050262425049520068688794604238349049149488\ 18373264705576411070464] |