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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 56 |
| 4 | 1056 |
| 5 | 25152 |
| 6 | 721792 |
| 7 | 24242048 |
| 8 | 934070016 |
| 9 | 40677025792 |
| 10 | 1978400285696 |
| 11 | 106415765626880 |
| 12 | 6277848492765184 |
| 13 | 403294366605090816 |
| 14 | 28037670640704192512 |
| 15 | 2098017767318156902400 |
| 16 | 168168589694078181900288 |
| 17 | 14378323356065959114047488 |
| 18 | 1306353644272598753321943040 |
[2,4,56,1056,25152,721792,24242048,934070016, 40677025792,1978400285696,106415765626880, 6277848492765184,403294366605090816, 28037670640704192512,2098017767318156902400, 168168589694078181900288, 14378323356065959114047488, 1306353644272598753321943040] |