A123214
Primes q such that (2^p + 1)/3 is prime, where p = Prime[q]; or primes in A123176[n].
Original entry on oeis.org
2, 3, 5, 7, 11, 31, 43, 1697, 12923, 13103, 77509
Offset: 1
A123176[n] begin {2, 3, 4, 5, 6, 7, 8, 9, 11, 14, 18, 22, 26, 31, 39, 43, ...}.
Thus
a(1) = 2, a(2) = 3, a(3) = 5, a(4) = 7, a(5) = 11, a(6) = 31, a(7) = 43.
A243979
Indices of Wagstaff primes.
Original entry on oeis.org
2, 5, 14, 124, 399, 4552, 15898, 203095, 37029521, 105973558438, 19140185454656173, 3827634977577891833517
Offset: 1
For n = 3 the third Wagstaff prime is A000979(3) = 43 and 43 is also the 14th prime number, so a(3) = 14.
- 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.
- Kim Walisch, Fast C++ prime counting function implementation (primecount).
- Wikipedia, Wagstaff prime.
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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
a(12) calculated using Kim Walisch's primecount and added by
Amiram Eldar, Sep 05 2024
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