A Japanese mathematician (? Fukimara or similar) described the numbers that reappear if their digits are summed, that number reversed and those added.
1729 adds to 19; 19 times 91 is 1729, the Hardy taxi number.
Many know 91 is 3 cubed plus 4 cubed; it is also 6 cubed plus -5 cubed.

A Japanese mathematician (? Fukimara or similar) described the numbers that reappear if their digits are summed, that number reversed and those added.

1729 adds to 19; 19 times 91 is 1729, the Hardy taxi number.

Many know 91 is 3 cubed plus 4 cubed; it is also 6 cubed plus -5 cubed.