# Advent calendar 2018

## Archive

Show me a random puzzle**Most recent collections**

#### Sunday Afternoon Maths LXVII

Coloured weightsNot Roman numerals

#### Advent calendar 2018

#### Sunday Afternoon Maths LXVI

Cryptic crossnumber #2#### Sunday Afternoon Maths LXV

Cryptic crossnumber #1Breaking Chocolate

Square and cube endings

List of all puzzles

## Tags

mean regular shapes cube numbers colouring christmas sum to infinity means graphs multiples money triangles sport planes functions parabolas spheres advent bases logic chess triangle numbers division polygons books chocolate sequences arrows cryptic clues perimeter area rugby geometry scales cards odd numbers shape coins factors calculus speed chalkdust crossnumber digits circles palindromes differentiation 2d shapes averages star numbers square roots integration 3d shapes folding tube maps surds doubling time taxicab geometry shapes probabilty games factorials symmetry grids routes dodecagons rectangles crossnumbers crosswords remainders prime numbers dates trigonometry percentages ave number integers people maths coordinates multiplication floors proportion clocks square numbers probability cryptic crossnumbers quadratics squares irreducible numbers complex numbers numbers sums unit fractions partitions indices ellipses wordplay perfect numbers pascal's triangle angles volume addition menace hexagons algebra lines dice fractions balancing## 6 December

This puzzle is inspired by a puzzle that Daniel Griller showed me.

Write down the numbers from 12 to 22 (including 12 and 22). Under each number, write down its largest odd factor*.

Today's number is the sum of all these odd factors.

* If a number is odd, then its largest odd factor is the number itself.