First awarded in 1936, the Fields Medal honours mathematicians under 40 every four years. It took until 2014 for a woman to receive it: Iran's Maryam Mirzakhani, for her work on the geometry of curved surfaces. She thought by covering huge sheets of paper with drawings, so much that her daughter believed she was painting. She died of cancer in 2017, aged 40.
How many different structures can you build with six classic 2-by-4 Lego bricks of the same colour? The company used to quote just over 102 million. In 2005, Danish mathematician Søren Eilers recounted everything by computer: 915,103,765 combinations. The official estimate had been too low by a factor of about nine.
Fold an A4 sheet in half and you get an A5 with the same proportions. That only works for one ratio between length and width: about 1.414, the square root of 2. The A0 format measures exactly one square metre, and A4 is a sixteenth of it. With standard 80-gram-per-square-metre paper, an A4 sheet therefore weighs exactly 5 grams.