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A243979 Indices of Wagstaff primes.

%I A243979 #26 Sep 05 2024 16:49:19
%S A243979 2,5,14,124,399,4552,15898,203095,37029521,105973558438,
%T A243979 19140185454656173,3827634977577891833517
%N A243979 Indices of Wagstaff primes.
%H A243979 Andrew R. Booker, <a href="https://t5k.org/nthprime/">The Nth Prime Page</a>.
%H A243979 Chris K. Caldwell, <a href="https://t5k.org/top20/page.php?id=67">Wagstaff</a>, The Top Twenty, The PrimePages.
%H A243979 Xavier Gourdon and Pascal Sebah, <a href="http://numbers.computation.free.fr/Constants/Primes/countingPrimes.html">Counting primes</a>.
%H A243979 Tomás Oliveira e Silva, <a href="https://sweet.ua.pt/tos/primes.html">Tables of values of pi(x) and of pi2(x)</a>.
%H A243979 Samuel S. Wagstaff, Jr., <a href="http://homes.cerias.purdue.edu/~ssw/cun/index.html">The Cunningham Project</a>.
%H A243979 Kim Walisch, <a href="https://github.com/kimwalisch/primecount">Fast C++ prime counting function implementation (primecount)</a>.
%H A243979 Wikipedia, <a href="http://en.wikipedia.org/wiki/Wagstaff_prime">Wagstaff prime</a>.
%F A243979 a(n) = A000720(A000979(n)).
%F A243979 A000040(a(n)) = A000979(n).
%e A243979 For n = 3 the third Wagstaff prime is A000979(3) = 43 and 43 is also the 14th prime number, so a(3) = 14.
%o A243979 (PARI) default(primelimit, 10^9); forprime(p=3, 31, q=(2^p+1)/3; if(isprime(q), print1(primepi(q)", "))) \\ _Jens Kruse Andersen_, Jun 22 2014
%Y A243979 Cf. A000040, A000720, A000978, A000979, A059305, A123176, A126614, A194810.
%K A243979 nonn,hard,more
%O A243979 1,1
%A A243979 _Omar E. Pol_, Jun 18 2014
%E A243979 a(11) from _Jens Kruse Andersen_, Jun 22 2014
%E A243979 a(12) calculated using Kim Walisch's primecount and added by _Amiram Eldar_, Sep 05 2024