# Christmas puzzle #1: Christmas tree sudoku

Puzzle #1 in our 2020 Christmas puzzle series

Here at Chalkdust, we like to celebrate Christmas as much as the next magazine for the mathematically curious, and what better way to celebrate than with a few yuletide mathematical puzzles. We have three for you, the first one you can find below, the second one will be published tomorrow (Christmas Day), and the final one the day after (Boxing Day). They are the perfect accompaniment to an warming hot chocolate and mince pie. Each puzzle is related to the previous one, so keep a hold of your solutions ready for the next day. We hope you enjoy giving them a go and the whole team wishes you a very merry Christmas!

## The rules

• Normal sudoku rules apply: you must complete the 9×9 grid with the digits 1 to 9 such that each digit appears exactly once in each row, column, and 3×3 block.
• The digits that appear on each thermometer must strictly increase as you move away from the bulb. The colours of the thermometers are purely decorative and do not affect the puzzle.
• The digits on the baubles are all even.
• The digits on the stars are all prime.

Here is a simple example:

## The puzzle

Make a note of the digits labelled by α, β, γ, δ, ε, ζ, η, θ, and λ (which are not necessarily distinct), they may be useful in the next puzzle!

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