These resistors are in series. Think of it of where the electrons can travel in the system. If there are multiple options for where they can travel then it is parallel, if there are no split paths (only one option) then it is series.
An example of a combination of resistors in parallel: The image you have above, but replace R2 with a wire that continues to the right to a battery. Then resistors R1 and R3 are in parallel.
