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 2005-08-07, 13:17 #1 robert44444uk     Jun 2003 Suva, Fiji 23·3·5·17 Posts Proth Riesel Drag Racing I have been looking recently at drag racing Proth (k.2^n+1 with fixed k) series and its corresponding Riesel series k.2^n-1 for the same k, with a view to finding the k which provides 100 primes for both series in the lowest series of n. To do so I have been thankful for Anand Nair's Payamx program, which sieves k which have no small factors either + or - up to a given factor. Of course, I might have just checked primorial values of k but using Anand's program allows greater granularity. I have been managing the large number of n to check with Maple 9, and checking the final higher values of n with NewPgen as my sieve and pfgw for the prime checking. The best result I have achieved so far is for the k most easily expressed as 3988838823*67#/1858202, for which the 100th prime is n=41653 for the + series and 20399 for the - series. There are a number of other interesting challenges I have set myself, including finding the lowest n for which there are 100 primes + or -, and the fastest I have achieved is n=4957853627*67#/1858202, with its 100th prime at n=909, although I expect to beat that rather easily as I explore lower values of n. Good candidates might have 25 primes in the first 30 n, 42 in the first 100, and 85 by n=500. Regards Robert Smith
 2005-09-24, 10:35 #2 robert44444uk     Jun 2003 Suva, Fiji 204010 Posts A slight improvement For those who are interested, a slight improvement in my previous posted record: k=62539727*47#/27791 has its 100th prime for the +series for n= 37907, and for the - series at n=33837 Regards Robert Smith

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