A243979 Indices of Wagstaff primes.

2, 5, 14, 124, 399, 4552, 15898, 203095, 37029521, 105973558438, 19140185454656173

Offset

1,1

Links

Table of n, a(n) for n=1..11.

Andrew R. Booker, The Nth Prime Page

C. Caldwell's The Top Twenty, Wagstaff.

Xavier Gourdon and Pascal Sebah, Counting primes

Tomás Oliveira e Silva, Tables of values of pi(x) and of pi2(x)

S. 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

Crossrefs

Cf. A000040, A000720, A000978, A000979, A059305, A123176, A126614, A194810.

Sequence in context: A214374 A284661 A097595 * A081483 A118478 A179675

Adjacent sequences: A243976 A243977 A243978 * A243980 A243981 A243982

Keyword

nonn,hard,more

Author

Omar E. Pol, Jun 18 2014

Extensions

a(11) from Jens Kruse Andersen, Jun 22 2014

Status

approved