"Lost Days 2022" appears to be a calendar for the coming year. But each month has some dates missing, or “lost”, defined by different mathematical series and simple code messages. January is missing prime numbers, February factors of 28, March the Fibonacci series, etc. Maybe you know someone who is mathematical and needs a Christmas present!
Packs flat and comes in an envelope with a key explaining the mathematical series or code messages used. Uses my "castellated spine" structure. £22 + p/p