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1729 and taxicabs

The Number 1729 (Source: Wikipedia (1729))

It was around the time of World War 1 in England when G.H. Hardy came to visit a young Indian mathematician named Srinivasa Ramanujan. The Indian had arrived in the country in 1914 and his weak constitution coupled with the lack of vegetarian food often left him much the worse for wear. Hardy later recalled this meeting as quoted below:

I remember once going to see him when he was ill at Putney. I had ridden in taxi cab number 1729 and remarked that the number seemed to me rather a dull one, and that I hoped it was not an unfavorable omen. "No," he replied, "it is a very interesting number; it is the smallest number expressible as the sum of two cubes in two different ways."

The two different ways that Ramanujan mentioned are as follows:
1³ + 12³ = 1729
9³ + 10³ = 1729

This anecdote led to numbers with such properties being named taxicab numbers. 1729 itself is now famously referred to as the Hardy-Ramanujan number and has even been used as a plot-point in the TV show Futurama!