Zig Zag Sequence

Continue the sequence with the correct number.


There is a list of numbers (1 - 9) that will be added in sequence ... can you know what the next number is?


   in the list there are:


in the easy level: between 2 and 4 numbers.

in the medium level: between 3 and 5 numbers.

in the hard level: between 3 and 10 numbers.