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A127956 Prime numbers p such that (2^p+1)/3 is composite. 11

%I

%S 29,37,41,47,53,59,67,71,73,83,89,97,103,107,109,113,131,137,139,149,

%T 151,157,163,173,179,181,193,197,211,223,227,229,233,239,241,251,257,

%U 263,269,271,277,281,283,293,307,311,317,331,337,349,353,359,367,373

%N Prime numbers p such that (2^p+1)/3 is composite.

%C If p-1 is squarefree, 2a(n) is the multiplicative order of 2 modulo every divisor d>1 of (2^p+1)/3. - _Vladimir Shevelev_, Jul 15 2008

%t a = {}; Do[c = (2^Prime[x] + 1)/3; If[PrimeQ[c] == False, AppendTo[a, Prime[x]]], {x, 2, 100}]; a

%Y Cf. A000979, A000978, A124400, A126614, A127955, A127957.

%K nonn

%O 1,1

%A _Artur Jasinski_, Feb 09 2007

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Last modified July 17 02:10 EDT 2019. Contains 325092 sequences. (Running on oeis4.)