Reminds me of when I used to sit in engineering class idly finding formulas, like 69!, that came as close as possible to exceeding the mantissa limits of my old IT calculator. Good times.
Fun With Very Large Numbers
Authors: Robert Baillie(Submitted on 19 May 2011)Abstract: We give an example of a formula involving the sinc function that holds for every N = 0, 1, 2, …, up to about 10^102832732165, then fails for all larger N. We give another example that begins to fail after about N ~ exp(exp(exp(exp(exp(exp(e)))))). This number is larger than the Skewes numbers.
via arxiv.org
Pedantry alert: mantissa is the "worthless" fraction; it was probably the exponent limit that you exceeded.
I remember doing the same 69! calculation when I was young.