I have interest in ontology of numbers. I know that the two main schools of thought regarding the metaphysical status of numbers are mathematical Platonism and mathematical Nominalism. But I wonder - What other schools of thought address the question of the ontology of Numbers? And, where may I find concise but yet profound introduction to this subject?
Here is a very good SEP entry that covers a lot of ground regarding the subject in a clear and informative manner: Platonism in the Philosophy of Mathematics. (It has 'Platonism' in the title but gives you a good idea about opposing views as well).