20th February

On this day in 1648, a letter from Pierre de Fermat through Frenicle de Bessy to Kenelm Digby reached John Wallis saying that Fermat had solved equations of the type

x^2 - Ay^2 = 1

for all non-square values up to 150. Thus begins the saga of the mis-naming of Pell's equation.

The postage stamp of one of today's mathematicians at THIS LINK was issued in 1981.