I enjoyed this too but then I'm a statistician so the other 48 weeks are tough haha. But I love how the Listener introduces me to new subjects.
This week I learnt three things:
1. That the length of Roman numerals bears no resemblance to their size. Obvious but never thought of that before and pretty crucial to this puzzle
2. That Roman numerals can only go up to 3999 (unless you use the medieval versions)
3. That Excel has a ROMAN() function that converts decimals to ROMAN (Kitsune you might be cursing yourself!)