Agree. Very satisfying. Got a little distracted by the unclued entry as we found 3 plausible moduli (or is it moduluses?). So it was the usual grind, generating gibberish until the right message emerged. For non-mathematicians, think the compiler’s preamble might have just illustrated how to deal with pairs like 28 or 29, using his example of 30.
Remember happy times over a beer in the pub in the late 70s as the locals competed!