''Ramanujan was recovering from his first bout of serious illness in a nursing home in Putney and Hardy had gone there by taxi to visit him.

Hardy (never much of a conversationalist) greeted the sick man abruptly with the words: "The number of the taxi-cab that brought me here was 1729. It seemed to me rather a dull number."

To which Ramanujan replied without hesitation: "Not at all, Hardy! It is a very interesting number. It is the smallest number expressible as the sum of two cubes in two different ways."

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''Ramanujan was recovering from his first bout of serious illness in a nursing home in Putney and Hardy had gone there by taxi to visit him.

Hardy (never much of a conversationalist) greeted the sick man abruptly with the words: "The number of the taxi-cab that brought me here was 1729. It seemed to me rather a dull number."

To which Ramanujan replied without hesitation: "Not at all, Hardy! It is a very interesting number. It is the smallest number expressible as the sum of two cubes in two different ways."

1729 can indeed be represented as 1³ + 12³ and as 9³ + 10³, and is the lowest integer for which such a combination is possible.

What intrigued me about the story was that someone could have such a familiarity with the integers that he would spontaneously recognise an attribute of an apparently "dull" or unprepossessing number as being susceptible of expression in a (for a mathematician) attractively patterned way.

Hardy and Ramanujan found a common language

"Every positive integer is one of Ramanujan's personal friends" was how Hardy's friend Littlewood described it.

Caring deeply about numbers and their properties may in part at least be something that runs in families. At the age of four, my eldest son used to wake in terror from a recurrent nightmare. He was on a wide sandy beach at low tide.

"I had to count the grains of sand," he would tell me, tearfully, "and I knew that I just wouldn't be able to do it."

Even at that age, numbers mattered to him intensely enough for him to dream about them. But just as in some families, fear of spiders is passed on to the children who witness their parents' alarm at an arachnid in the bath tub, so terror of mathematics can be passed on from generation to gen