title: why are composite numbers bad for hashing by division?
body: <p>This is my first question on stackflow. As you can tell, I am new to learning algorithms and data structure. </p>
  
  <p>When using the division method for create a hash function (i.e. h(k) = k mod m), one is advised (e.g. by CLRS) to use a prime number not too close to a power of 2 for the divisor m. Could someone kindly explain to me why a choice of m to be a <strong>composite</strong> number is bad?</p>