23rd August

On this day in 1638, René Descartes, in a letter to Mersenne, proposed his folium (

x^3 + y^3 = 2axy

) as a test case to challenge Fermat's differentiation techniques. To Descartes' embarrassment, Fermat's method worked better than his own.
See THIS LINK

The postage stamp of one of today's mathematicians at THIS LINK was issued in 1961.