should I mentioned unrelated research experience in SOP?

[bemonocled]

I'm applying for grad school this fall for math, but I spent my first 3 years as a physics major. I worked in an experimental physics lab for 2 of those years, and it appears on my transcript as research credit. I'm not getting a letter of recommendation from the professor I worked under and its not math related, so should I bother mentioning it in my statement of purpose? I'm worried that it will look strange that I have 2 years of physics research credit on my transcript but I never even mention it in the statement of purpose. I can talk plenty about my math research already, so I'm not lacking about research to talk about. Opinions appreciated.

[MattW]

If you're worried about it then just put a single sentence mentioning what you did.