In 1202, Fibonacci presented his famous sequence through a problem about rabbits. But centuries earlier, Indian scholars such as Virahanka and later Hemachandra already knew it. Their question: how many rhythms can be built from short and long syllables, a long one lasting as much as two short ones? The answer follows exactly 1, 2, 3, 5, 8, 13 and so on: here, mathematics was born from poetry.
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.