Archimedes named a number big enough to count every grain of sand in the universe
Ancient Greeks had no word for a number larger than a 'myriad myriad' (100 million) -- anything bigger was simply 'uncountable.' So when someone claimed the sand needed to fill the whole universe was too many to ever count, one mathematician set out to prove them wrong. Could he actually name a number big enough, using only the mathematics of his day?
Reveal the answer
Yes -- in The Sand Reckoner, Archimedes invented a new system for naming enormous numbers, combined it with an early estimate of the size of the cosmos, and calculated that fewer than 10^63 grains of sand would fill a universe-sized sphere. It also preserves the only surviving reference to Aristarchus's heliocentric theory.