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 A000979 Wagstaff primes: primes of form (2^p + 1)/3. (Formerly M2896 N1161) 24

%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 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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