[R] extremely simple "for loop" question

[Brian Quinif]

I am sorry to ask such a simple question, but my knowledge of
programming language is extremely limited, and I couldn't find the
answer in any of the normal resources.

I want to do a for loop in which m takes on the values 1, 5, 10, 15,
20.  What is the syntax for doing that?

I had been doing a loop for m in 1:20, but I only want those values above.

Thanks,

Brian