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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 20 |
| 3 | 464 |
| 4 | 17024 |
| 5 | 1632256 |
| 6 | 499253248 |
| 7 | 211076251648 |
| 8 | 432343353393152 |
| 9 | 1184049383163822080 |
| 10 | 10988005485374521475072 |
| 11 | 249434575164299910905331712 |
| 12 | 9434727599158183495094688022528 |
[1,4,20,464,17024,1632256,499253248,211076251648, 432343353393152,1184049383163822080, 10988005485374521475072, 249434575164299910905331712, 9434727599158183495094688022528] |