# 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

cryptic clues triangles odd numbers complex numbers balancing irreducible numbers multiplication percentages probabilty sequences number circles floors square numbers perfect numbers algebra surds sport ellipses cards digits multiples integration folding tube maps quadratics grids numbers planes crosswords cryptic crossnumbers coins routes triangle numbers bases calculus shapes functions dates time lines unit fractions shape dodecagons factors star numbers doubling factorials 3d shapes volume differentiation menace angles averages symmetry square roots speed games proportion addition arrows hexagons means partitions dice prime numbers people maths wordplay sum to infinity geometry palindromes sums spheres integers squares coordinates polygons money chess pascal's triangle cube numbers taxicab geometry regular shapes probability perimeter logic christmas fractions mean ave indices 2d shapes graphs books parabolas clocks chalkdust crossnumber colouring chocolate crossnumbers advent area rugby division rectangles trigonometry remainders scales## 17 December

For \(x\) and \(y\) between 1 and 9 (including 1 and 9), I write a number at the co-ordinate \((x,y)\): if \(x\lt y\), I write \(x\); if not,
I write \(y\).

Today's number is the sum of the 81 numbers that I have written.