For this sequence to be arithmetic each term must be separated by a common difference. In other words

Since then the series is not arithmetic

More it to be geometric then the ratio of each successive term must be equal:

so it is not geometric either.

From what I can gather this is of the form but I do not know where to go from there but hopefully someone else may be able to take it further

edit:are you told howxandarelate to the sequence?