John Pell

John Pell (1611–1685) was an English mathematician, cryptographer, and sometime diplomat who is the proud owner of an equation he had almost nothing to do with. He was a real scholar — he taught maths, decoded secret messages, and even served as an envoy to Switzerland — but his lasting fame rests on one of the most famous misattributions in the whole history of mathematics.

The famous result

Say the words Pell's equation — the deceptively simple x^2 - n y^2 = 1 — and every number theorist knows exactly what you mean. Finding whole-number solutions is a surprisingly deep puzzle, linked to continued fractions and to how well irrational numbers can be approximated by fractions. It's a cornerstone of the study of Diophantine equations, and it sits under Pell's name forever.

The blame goes to Euler, one of the greatest mathematicians ever, who read a paper, misremembered who had done the work, and casually attached Pell's name to the equation. The real pioneers were Fermat, who challenged others to solve it, and Lord Brouncker, who found a method — while the Indian mathematician Brahmagupta and later Bhāskara had cracked cases of it a thousand years earlier. Poor Pell contributed essentially nothing, yet Euler's slip was so influential that the name stuck for good. Immortality by clerical error.