Had 1729 caught your eye before Hardy's visit, or did you truly calculate it in an instant?

I had seen it before, sir. Not the number 1729 itself perhaps, but the pattern it belongs to — I had worked through the sums of two cubes in my notebooks in Madras. When you are filling pages with such things, the small cases become like old friends. When Professor Hardy said the number was dull, I knew at once it could not be. Every number speaks if you have sat with it long enough. That one whispers 1³ + 12³ and also 9³ + 10³. The smallest to do so. It was not a feat of instant calculation. It was recognition.