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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | -2 |
| 2 | -4 |
| 3 | -20 |
| 4 | -140 |
| 5 | -1192 |
| 6 | -11656 |
| 7 | -127072 |
| 8 | -1517480 |
| 9 | -19624400 |
| 10 | -272656064 |
| 11 | -4046157472 |
| 12 | -63844717184 |
| 13 | -1067307017600 |
| 14 | -18846094327360 |
| 15 | -350578477836160 |
| 16 | -6854465726916640 |
| 17 | -140564170444594880 |
| 18 | -3017526392523529600 |
| 19 | -67690323794750627200 |
[1,-2,-4,-20,-140,-1192,-11656,-127072,-1517480, -19624400,-272656064,-4046157472,-63844717184, -1067307017600,-18846094327360,-350578477836160, -6854465726916640,-140564170444594880, -3017526392523529600,-67690323794750627200] |