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URL: https://oeis.org/A243979

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A243979
Indices of Wagstaff primes.
0
2, 5, 14, 124, 399, 4552, 15898, 203095, 37029521, 105973558438, 19140185454656173, 3827634977577891833517
OFFSET
1,1
LINKS
Andrew R. Booker, The Nth Prime Page.
Chris K. Caldwell, Wagstaff, The Top Twenty, The PrimePages.
Xavier Gourdon and Pascal Sebah, Counting primes.
Tomás Oliveira e Silva, Tables of values of pi(x) and of pi2(x).
Samuel S. Wagstaff, Jr., The Cunningham Project.
Wikipedia, Wagstaff prime.
FORMULA
a(n) = A000720(A000979(n)).
A000040(a(n)) = A000979(n).
EXAMPLE
For n = 3 the third Wagstaff prime is A000979(3) = 43 and 43 is also the 14th prime number, so a(3) = 14.
PROG
(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
KEYWORD
nonn,hard,more
AUTHOR
Omar E. Pol, Jun 18 2014
EXTENSIONS
a(11) from Jens Kruse Andersen, Jun 22 2014
a(12) calculated using Kim Walisch's primecount and added by Amiram Eldar, Sep 05 2024
STATUS
approved