Number Gossip

(Enter a number and I'll tell you everything you wanted to know about it but were afraid to ask.)

Unique Properties of 18

  • 18 is the smallest difference between an emirp and its reverse
  • 18 is the only number that is twice the sum of its digits
  • 18 is the only area of a rectangle with distinct integer sides such that the perimeter of the rectangle equals the area
  • 18 is the only integer n such that n3 and n4 together contain each of the ten digits once
  • The 18-Point problem asks to choose a sequence of points on an interval such that the first two are in different halves of the interval,the first three are in different thirds, and so on. The result is that it is impossible to find 18 such points

Common Properties of 18