is a pattern. The problem is finding what the setter had in mind, which
means a rule that is simple and obvious when you find it.
I see no simple pattern here, but that does not mean that there is none.
If this is a maths problem then there probably is a simple pattern here.
If this is a puzzle form a non-math web site then the only simplicity may
be in the mind of the setter.
The online encyclopedia of integer sequences does not recognise it, so
if there is a simple pattern it is not a mathematical one.