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| n | a(n) |
|---|---|
| 0 | -1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 32 |
| 4 | 210 |
| 5 | 1536 |
| 6 | 12012 |
| 7 | 98304 |
| 8 | 831402 |
| 9 | 7208960 |
| 10 | 63740820 |
| 11 | 572522496 |
| 12 | 5209363380 |
| 13 | 47915728896 |
| 14 | 444799488600 |
| 15 | 4161823309824 |
| 16 | 39209074920090 |
| 17 | 371626340253696 |
| 18 | 3541117629057540 |
[-1,2,6,32,210,1536,12012,98304,831402,7208960, 63740820,572522496,5209363380,47915728896, 444799488600,4161823309824,39209074920090, 371626340253696,3541117629057540] |