Puzzles
The dullest number in a taxi's licence plate
Visiting a sick Srinivasa Ramanujan in hospital, G. H. Hardy mentioned he'd arrived in taxi number 1729, calling it 'rather a dull number'. Ramanujan disagreed instantly. What did he see in it, without doing any calculation on paper?
Reveal the answer
1729 is the smallest number expressible as the sum of two cubes in two different ways: 1³ + 12³ = 1,729 and 9³ + 10³ = 1,729. Ramanujan reportedly saw this immediately from memory. Such numbers are now called 'taxicab numbers' in his honour.
— Robert Kanigel, The Man Who Knew Infinity — Biography of Ramanujan, 1991; anecdote recorded by G. H. Hardy
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