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%I #6 Jun 07 2021 15:07:01
%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
%t Select[Prime[Range[2,100]],CompositeQ[(2^#+1)/3]&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jun 07 2021 *)
%Y Cf. A000979, A000978, A124400, A126614, A127955, A127957.
%K nonn
%O 1,1
%A _Artur Jasinski_, Feb 09 2007
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