19 is only 1 away from 20, so you prefer to start by multiplying 20 times 5, which equals 100. Then we need to take away a squadron of 5, because there are actually only 19 squadrons, not 20. 100 take ...

David Harvey receives funding from the Australian Research Council. Around 1956, the famous Soviet mathematician Andrey Kolmogorov conjectured that this is the best possible way to multiply two ...