I dunno what's its limit, but have you tried using double data-type?
Although in most of math functions, you'll have to prefix them w/ Math.
if you want the calculation itself to use double values!

I doubt even a double would store up to 100,000 digits of Pi.
You may need to create your own data structure to do it... one that keeps track of the specific digits.

Thanks! great suggestion, but Im going to just dump all these numbers into a String

Or use Java's BigDecimal (and check out BigInteger too).

Gr8 advise, PhiLho!

Also, you may want to use a separate thread (or more) to do the calculation.
Lest Processing API may slow down the whole thing!