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 2020-08-15, 11:21 #1 Ensigm   Aug 2020 11410 Posts PRP residue question If a mersenne number has more than two prime factors, i.e. Mn = A * B * composite_factor , are the residues from running PRP on Mn/A and Mn/A/B the same? Asking this because I saw M8325613, where M8325613/4504206586679 and M8325613/4504206586679/121878456335252812193 gave the same residue 88A96FEB41BFB7FD. Last fiddled with by Ensigm on 2020-08-15 at 11:22
 2020-08-15, 12:22 #2 ATH Einyen     Dec 2003 Denmark 2·7·229 Posts Yes, if 1 type 5 PRP test has been done and another factor is found then only 1 type 5 test is needed because it gives the same residue because type 5 test is doing a^(N*knownfactors-1) (mod N). So if Mn=A*B*C and factor A is found first then N=B*C and knownfactors=A, so it is doing: a^(B*C * A - 1 ) (mod B*C) Later when factor B is found then N=C and knownfactors=A*B, so it is doing: a^(C * A*B - 1) (mod C) so the exponent is the same and because C is a factor of B*C it will give the same 64bit residue. The full residues are not equal but if we call the first one R1 and second one R2 then: R1 (mod C) = R2. Last fiddled with by ATH on 2020-08-15 at 13:09

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