McCarthy 91

Think Recursion is cool ? Check out the McCarthy 91 recursive function. Conceived by computer scientist John McCarthy, it takes the value 91 for all positive integers less than 102. Here is the C implementation ,

/* McCarthy 91 Recursive Function -
 * for 0 <= n < 102,
 * M(n) =  { n - 10,     if n  > 100
 *         { M(M(n+11)), if n <= 100
 */
unsigned int M(unsigned int n)
{
  if (n > 100)
    return n - 10;
  else {    
    return M(M(n+11));
  }
}