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%I A177210 #10 Feb 16 2021 02:09:45
%S A177210 26,33,35,39,46,58,62,65,93,94,111,118,119,133,134,146,155,161,178,
%T A177210 183,202,206,209,214,219,226,235,237,247,249,253,259,267,287,291,295,
%U A177210 299,334,335,341,362,377,382,386,391,393,395,407,422,445,447,451,453,478
%N A177210 Numbers k that are the products of two distinct primes such that 2*k-1 are also products of two distinct primes.
%e A177210 26 is a term because 26 = 2*13 and 2*26 - 1 = 51 = 3*17;
%e A177210 33 is a term because 33 = 3*11 and 2*33 - 1 = 65 = 5*13.
%t A177210 f[n_]:=Last/@FactorInteger[n]=={1,1}; lst={};Do[If[f[n]&&f[2*n-1],AppendTo[lst,n]],{n,0,4*6!}];lst
%t A177210 Select[Range[500],PrimeNu[#]==PrimeOmega[#]==PrimeNu[2#-1] == PrimeOmega[ 2#-1] == 2&] (* _Harvey P. Dale_, May 23 2014 *)
%Y A177210 Cf. A006881.
%K A177210 nonn
%O A177210 1,1
%A A177210 _Vladimir Joseph Stephan Orlovsky_, May 04 2010

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