This a series of questions that are created by myself.
I will give a hint in 24 hours and my answer in 3 days given that nobody could answer my question.
Here is question 5:
342,765,?,242325 (It seems like it is easy and might have several answers but there is only one answer and the logic must be the neatest) $$$$ If you guys want some extremely challenging questions. Please check these two questions posted by me.