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%I #2 Mar 30 2012 17:34:27
%S 3,5,7,11,29,31,127,131,8191,131071,524287,536870909,2147483647,
%T 2305843009213693951,147573952589676412931,
%U 618970019642690137449562111,162259276829213363391578010288127
%N Primes of the four types: {2^Prime[n] - 1, 2^Prime[n] + 1, 2^Prime[n] - 3, 2^Prime[n] + 3}.
%F a(n) = If[PrimeQ[{2^Prime[n] - 1, 2^Prime[n] + 1, 2^Prime[n] - 3, 2^Prime[n] + 3}, which of them is prime]
%t f[n_] := If[PrimeQ[2^Prime[n] - 1] || PrimeQ[2^Prime[n] + 1] || PrimeQ[2^Prime[n] - 3] || PrimeQ[2^Prime[n] + 3], {2^Prime[n] - 1, 2^Prime[n] + 1, 2^Prime[n] - 3, 2^Prime[n] + 3}, {}]; a = Flatten[Table[f[n], {n, 1, 100}]]; Union[Flatten[Table[If[PrimeQ[a[[n]]], a[[n]], {}], {n, 1, Length[a]}]]]
%K nonn,uned
%O 1,1
%A _Roger L. Bagula_, Sep 18 2008
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