title: Determine the adjacency of two fibonacci number
body: <p>I have many fibonacci numbers, if I want to determine whether two fibonacci number are adjacent or not, one basic approach is as follows:</p>
  
  <ol>
  <li>Get the index of the first fibonacci number, say i1</li>
  <li>Get the index of the second fibonacci number, say i2</li>
  <li>Get the absolute value of i1-i2, that is |i1-i2|
  If the value is 1, then return true.
  else return false.</li>
  </ol>
  
  <p>In the first step and the second step, it may need many comparisons to get the correct index by using accessing an array.</p>
  
  <p>In the third step, it need one subtraction and one absolute operation.</p>
  
  <p>I want to know whether there exists another approach to quickly to determine the adjacency of the fibonacci numbers.</p>
  
  <p>I don't care whether this question could be solved mathematically or by any hacking techniques.</p>
  
  <p>If anyone have some idea, please let me know. Thanks a lot!</p>