2005-03-07, 02:35 #4 geoff     Mar 2003 New Zealand 13·89 Posts It is also possible to use pfgw to test a small range without sieving first, but just trial factoring each candidate before the PRP test. Reserve your exponent as before, say k=2822 with nmin=54000 from the Sierpinski thread, then create this file (called 2822.txt say) with a text editor Code: ABC2 2822*5^\$a+1 a: from 54000 to 55000 Then run pfgw with the command line 'pfgw -f 2822.txt'. That is it. If there are any probable primes in the range 54000 to 55000 then they will be written to the file pfgw.log. For small ranges this is fine, but for large ranges sieving is much more efficient. pfgw speed for testing these numbers depends on which version you use for which hardware. For SSE2 machines I think you will need a quite recent version to get anywhere near the prp3 speeds.