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Old 2016-03-06, 07:06   #5
Batalov
 
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"Serge"
Mar 2008
Phi(4,2^7658614+1)/2

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43*71^n+c has many c values that generate all-composite sequences; they have a so-called covering set. But a few c values are working fine, e.g. c=4.

For kicks and giggles I sieved the c=4 series and ran it for a while. There are a few small primes (43*71^0+4, 43*71^4+4, 43*71^144+4, 43*71^784+4) and then a larger unprovable PRP: 43*71^38292+4 (submitted to PRPtop)
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Re: "Error opening file input.txt"
Check where you put the input.txt file. Is it in the same folder as the pfgw executable? If not - provide the full path, or move it in the same folder.
Then put "-f -l input.txt" in the text window of Win64Pfgw.exe.
Works fine here, and quickly finds a few tiny primes
24*181^14+229
24*181^51+229
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