title: Commutativity of XOR and mod
body: <p>So when exploring hash functions I noticed the following equation:</p>
  
  <p><code>((129*N)^prev)%256 = ((129*N)%256)^prev</code></p>
  
  <p>For any number <code>N, prev</code> between 0 and 255. Basically you can drag the mod operation out without changing the result, and it only works for number 129. Can somebody maybe tell me what is so special about 129?</p>