What’s the largest number that can be expressed in Roman numerals? If no single letter can appear more than three times in a row, then the highest we can go is 3,999, or MMMCMXCIX.

These 3,999 values contain in total 30,000 characters, and, pleasingly, reader Ian Duff finds that 5,600 are Is, 2,000 are Vs, 6,000 are Xs, 2,000 are Ls, 6,000 are Cs, 2,000 are Ds, and 6,400 are Ms.

(Thanks, Ian.)