I think his first example was a recursive function like:

  if !(mod(x,2) {
   if (x == 1) return true  else return false;
  }else return is_power_of_2(x/2);

or

  if !(mod(x,2) {
   if (x == 1) return true;
   if ((x > 1) || (x == 0)) return false;
   return is_power_of_2(x * 2);
  }else if (x > 2) return is_power_of_2(x/2) else return false;

PS: 2^0 = 1 and 2^-1 so you could have 3 versions of this fuction.