Whilst a dictionary search shows that the word is singular but plural in form, it is most commonly used (in my experience) with a verb in singular form.
Math(ematic)s is my least favourite subject.
Math(ematic)s is really hard.
This Ngram viewer helps:
EDIT: As @Araucaria points out, the "mathematics are" examples in the Ngram above are not really relevant. See his comment below.