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%I M2896 N1161
%S 3,11,43,683,2731,43691,174763,2796203,715827883,2932031007403,
%T 768614336404564651,201487636602438195784363,
%U 845100400152152934331135470251,56713727820156410577229101238628035243,62357403192785191176690552862561408838653121833643
%N Wagstaff primes: primes of form (2^p + 1)/3.
%C Also, the primes with prime indices in the Jacobsthal sequence A001045.
%C Indices n such that (2^n + 1)/3 is prime are listed in A000978. - _Alexander Adamchuk_, Oct 03 2006
%D Editor's Note, Math. Mag., 27 (1954), 157.
%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H T. D. Noe, <a href="/A000979/b000979.txt">Table of n, a(n) for n=1..20</a>
%H C. Caldwell's The Top Twenty, <a href="http://primes.utm.edu/top20/page.php?id=67">Wagstaff</a>.
%H S. S. Wagstaff, Jr., <a href="http://homes.cerias.purdue.edu/~ssw/cun/index.html">The Cunningham Project</a>.
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Wagstaff_prime">Wagstaff prime</a>
%t Select[ Array[(2^# + 1)/3 &, 190], PrimeQ] [From _Vladimir Joseph Stephan Orlovsky_, Apr 03 2010]
%o (Haskell)
%o a000979 n = a000979_list !! (n-1)
%o a000979_list = filter ((== 1) . a010051) a007583_list
%o -- _Reinhard Zumkeller_, Mar 24 2013
%Y Cf. A000978, A049883, A001045, A127962.
%Y Cf. A010051; subsequence of A007583.
%K nonn
%O 1,1
%A _N. J. A. Sloane_.
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