My view is that mind, matter, and mathematical objects are all that exist. What is the name of that view? Dualism is the view that both mind and matter exist. So, perhaps my view should be called Trialism, but that doesn't seem to be a real word. So, is there a standard name in the philosophical literature for my belief?
Dualism is the view about X that there are two X. Likewise, monism is a view that there is one X, nihilism - no X, pluralism - >2 X.
When talking about mind, there are two kinds of dualism - substance dualism and property dualism. Under substance dualism there are two substances - material and mental; under property dualism there are two kinds of properties - material and mental.
Math is typically viewed as something other than a substance or a property. The most widespread view under which math exists is called platonism. The shortest you can call such view will have to be "substance (or property) dualism + platonism."
If you still want to have math as a substance, you can have three substances (material, mind, and math), so the view can be called substance trialism or substance pluralism. I am not aware if there are any coined names for such view.