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 2007-01-05, 18:55 #4 masser     Jul 2003 wear a mask 23·191 Posts You can use NewPGen to figure out some of the lowest Riesel/Sierpinski numbers. Use the "k*b^n+/1 with k fixed" sieves, and then use the "sieve until" option. Sieve up to p=1000 (or a million - something that doesn't take too long), and then have it update k and start again. If this is done correctly, NewPGen will sieve k=1, 2, 3, and so on and create files 1.txt, 2.txt, 3.txt, etc. Sieve over a relatively small n set (1<=n<=2000) to keep the files small. Then just keep an eye on the size of the files - when you find one with size 0 - you've PROBABLY found a Riesel/Sierpinski number; do some fun math to figure out the covering set. This method is sloppy, inefficient, etc.... but it's easy to set up and run. The alternative is to do some careful input file creation with PFGW or your own coding. There's also a tool (psieve is what I think it's called) out there for calculating the weights of certain sequences. I think it works for k*b^n+/-1, with bases other than 2. You can fix b and loop through many k values and then look for sequences with weight 0. Actually, now that I am thinking of it, this is probably the best way (without actually doing the math) to find the Sierpinski/Riesel numbers for other bases. Hope this helps those of you interested... best regards, masser Last fiddled with by masser on 2007-01-05 at 18:57