I'm trying to iterate through all the combinations of pairs of positive long integers in Java and testing the sum of their cubes to discover if it's a Fibonacci number. I'm currently doing this by using the value of the outer loop variable as the inner loop's upper limit, with the effect being that the outer loop runs a little slower each time. Initially it appeared to run very quickly--I was up to 10 digits within minutes. But now after 2 full days of continuous execution, I'm only somewhere in the middle range of 15 digits. At this rate it may end up taking a whole year just to finish running this program. The code for the program is below:

import java.lang.*;
import java.math.*;

public class FindFib
{
 public static void main(String args[])
 {
  long uLimit=9223372036854775807L;   //long maximum value
  BigDecimal PHI=new BigDecimal(1D+Math.sqrt(5D)/2D);  //Golden Ratio

  for(long a=1;a<=uLimit;a++)    //Outer Loop, 1 to maximum
   for(long b=1;b<=a;b++)     //Inner Loop, 1 to current outer
   {
    //Cube the numbers and add
    BigDecimal c=BigDecimal.valueOf(a).pow(3).add(BigDecimal.valueOf(b).pow(3));
    System.out.print(c+" ");  //Output result
    //Upper and lower limits of interval for Mobius test: [c*PHI-1/c,c*PHI+1/c]
    BigDecimal d=c.multiply(PHI).subtract(BigDecimal.ONE.divide(c,BigDecimal.ROUND_HALF_UP)),
     e=c.multiply(PHI).add(BigDecimal.ONE.divide(c,BigDecimal.ROUND_HALF_UP));
    //Mobius test: if integer in interval (floor values unequal) Fibonacci number!
    if (d.toBigInteger().compareTo(e.toBigInteger())!=0)
     System.out.println();    //Line feed
    else
      System.out.print("\r");    //Carriage return instead
   }
  //Display final message
  System.out.println("\rDone.                                                                                 ");
 }
}

Now the use of BigDecimal and BigInteger was delibrate; I need them to get the necessary precision. Is there anything other than my variable types that I could change to gain better efficiency?