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%I #8 Sep 15 2018 19:30:28
%S 171,10923,699051,11184811,44739243,178956971,2863311531,11453246123,
%T 45812984491,183251937963,733007751851,11728124029611,46912496118443,
%U 187649984473771,750599937895083,3002399751580331,12009599006321323
%N Nonprime numbers of the form 1 + Sum_{k=1..m} 2^(2*k - 1).
%C Prime numbers of the form 1 + Sum_{k=1..m} 2^(2*n - 1) is A000979. Numbers x such that 1 + Sum_{k=1..m} 2^(2*n - 1) is prime for n=1,2,...,x is A127936. A127955 is probably a subset of the present sequence.
%t a = {}; Do[c = 1 + Sum[2^(2n - 1), {n, 1, x}]; If[PrimeQ[c] == False, AppendTo[a, c]], {x, 1, 50}]; a
%t Select[Table[Sum[2^(2k-1),{k,n}]+1,{n,50}],!PrimeQ[#]&] (* _Harvey P. Dale_, Dec 23 2017 *)
%Y Cf. A000979, A000978, A124400, A126614, A127955, A127956, A127957, A127958, A127936.
%K nonn
%O 1,1
%A _Artur Jasinski_, Feb 09 2007
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