Brain Game: Legal Twice Over

Your intrepid Brain Games composer turned 42 years old on Sunday. You Douglas Adams fans tell me - does that mean I should understand the meaning of life, the universe, and everything? Anyway, I went looking for a puzzle that included "42" in the mix, and I found one that's perfect for Math Monday. Good luck!

What's the next number in this sequence?

1, 2, 6, 42, 1806, ...?

Here is the SOLUTION.