OK, not quite koans, but worth some time if you are so inclined:

Where were the 1 million digits of pi that we have calculated (or for that matter the unending string of numbers that are embedded in pi) before we invented numbers?

Same koan:

Where was the unending number we label “e” that is it’s own differential and integral before we invented calculus?

Similar koan:

For both pi and e, where are all those unending digits now?

Similar koan:

How can there be a square root of -1 when any two negative numbers multiplied is a positive number? We call this number “i” and it is essential in the mathematics of quantum physics that is at the heart of all scientific thinking.

I can go on and on, but maybe you get the point.