Hard Series

What is the next number in this series?

4,12,84,3612....




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Which number should replace the question mark?

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On a windy rainy night , I was driving in my car.
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Amazing Facts

No Solution

In 2007, a puzzle was released and $2 million prizes were offered for the first complete solution. The competition ended at noon on 31 December 2010, with no solution being found. Wiki