
 square root of 2 
  It was the first number shown to be what is now known as an irrational number (a number that can't be written in the form a/b, where both a and b are integers.) This discovery was made by Pythagoras or, at any rate, by the Pythagorean group that he founded. 
  The square root of 2 is the length of the hypotenuse (longest side) of a right triangle whose other two sides are each one unit long. 
  Squaring each of these numbers gives 1, 36, 1225, 41616, 1413721, 48024900, 1631432881,..., each of which is also a triangular number. 
 www.daviddarling.info /encyclopedia/S/square_root_of_2.html (334 words) 
