# 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

folding tube maps factorials geometry perfect numbers polygons angles planes differentiation doubling shape rectangles surds people maths square roots money books chalkdust crossnumber coins remainders crosswords calculus menace volume clocks wordplay integration chess sum to infinity 3d shapes probabilty dodecagons taxicab geometry colouring regular shapes trigonometry time complex numbers symmetry circles indices logic balancing spheres numbers probability shapes integers fractions triangle numbers coordinates sequences sums christmas star numbers means cards squares palindromes ellipses cryptic clues arrows games ave cube numbers parabolas functions bases digits multiplication hexagons graphs cryptic crossnumbers averages quadratics irreducible numbers advent percentages mean square numbers number dice proportion prime numbers scales 2d shapes multiples dates routes speed rugby crossnumbers addition algebra unit fractions pascal's triangle floors partitions grids chocolate division factors triangles area lines odd numbers sport perimeter## 20 December

Today's number is the sum of all the numbers less than 40 that are not factors of 40.