[posterboy]

>Does this get us into the question of whether anything mathematical exists before anyone (or anysomething) first thought of it

No, because you can't ask for it's existence, before you thought of it.

>exists even when no-one is currently thinking of it

Again, who cares, it's by definition undefined, null, niente, the inbetween state of a ternary logic.

>I can imagine things

You can't will a pot of gold into existence by mere imagination, but you can't imagine an idea without it's inherint structure being real.

I'll admit, that's a simplistic outlook, but I wasn't encouraging a complicated discusion.