title: How to compute a^^b mod m?
body: <p>I have to compute efficiently a^^b mod m for large values of a,b,m&lt;2^32 <br>
  where ^^ is the tetration operator: 2^^4=2^(2^(2^2)) <br></p>
  
  <p>m is not a prime number and not a power of ten.<br></p>
  
  <p>Can you help?</p>