He asked for my number. What does that mean?

If a guy asks for you number is he definitely interested in you romantically or is there the possibility that he just wants to be friends? There is a guy that lives on my floor in my university dorm. We talk occasionally and he's very nice. Do you think that he asked for my number because he is interested in me romantically? He told me to text him if I went to this after party. I didn't end up texting him but he texted me. But when I invited him to hang out (which was at like 3 am when we both got home) he said he was tired. Since then we Haven't really talked. Should I invite him to come out with me and my friends one night?
He asked for my number. What does that mean?
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