In Daniel Tammet's mind, three is a dotted green crescent moon shape, one is a sort of white sunburst and four is a blue boomerang. Every number has a distinct color and shape, making the number pi, which begins with 3.14, unfold like a beautiful poem. For math enthusiasts around the world, March 14 (3-14) is Pi Day, honoring the number pi, which is the ratio of circumference to diameter of a circle. On Thursday, Tammet is promoting France's first Pi Day celebration at the Palace of Discovery science museum in Paris. Tammet's relationship to this number is special: At...