Why 1 isn't a Prime Number? And how long has it been a number? An engineer friend of mine recently surprised me by saying he wasn’t sure whether the number 1 was prime or not. I was surprised because among mathematicians, 1 is universally regarded as non-prime. The confusion begins with this definition a person might give of “prime”:  a prime number is a positive whole number that is only divisible by 1 and itself . The number 1 is divisible by 1, and it’s divisible by itself. But  itself  and  1  are not two distinct factors. Is 1 prime or not? When I write the definition of prime in an article, I try to remove that ambiguity by saying a prime number has exactly two distinct factors, 1 and itself, or that a prime is a whole number greater than 1 that is only divisible by 1 and itself. But why go to those lengths to exclude 1? My mathematical training taught me that the good reason for 1 not being considered prime is the fundamental theorem of arithmetic, which states that every nu

The Math of Social Distancing Is a Lesson in Geometry The GEOMETRY  of Social Distance By PASUPULETI NARENDRA SWAMY  July 13, 2020 How to safely reopen offices, schools and other public spaces while keeping people six feet apart comes down to a question mathematicians have been studying for centuries. 4 READ LATER BIG MOUTH  for NaReN Maths  Sphere packing might seem like a topic only a mathematician could love. Who else could get excited about finding the most efficient way to arrange circles in the plane, or spheres in space? But right now, millions of people all over the world are thinking about this very problem. Determining how to safely reopen buildings and public spaces under social distancing is in part an exercise in geometry: If each person must keep six feet away from everyone else, then figuring out how many people can sit in a classroom or a dining room is a question about packing non-overlapping circles into floor plans. Graphics by Samuel Velasco/Quanta Magazine Of cours