A000355 Primes p == 3, 9, 11 (mod 20) such that 2p+1 is also prime.

3, 11, 23, 29, 83, 89, 131, 191, 251, 431, 443, 491, 509, 683, 743, 809, 911, 1031, 1049, 1103, 1223, 1229, 1289, 1409, 1451, 1511, 1583, 1811, 1889, 1931, 2003, 2063, 2069, 2129, 2351, 2543, 2549, 2903, 2963, 2969, 3023, 3329, 3389, 3449, 3491, 3623, 3803

Offset

1,1

Comments

a(n) = (A000353(n)-1)/2. - Reinhard Zumkeller, Feb 10 2009

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

Robert A. J. Matthews, Maximally periodic reciprocals, Bull. Institute of Mathematics and Its Applications, vol. 28, p. 147-148, 1992.

Maple

q:= p-> irem(p, 20) in {3, 9, 11} and andmap(isprime, [p, 2*p+1]):
select(q, [$1..10000])[];  # Alois P. Heinz, Oct 31 2023

Mathematica

Select[Prime[Range[1000]], MatchQ[Mod[#, 20], 3|9|11] && PrimeQ[2#+1]&] (* Jean-François Alcover, Feb 07 2016 *)

Prog

(PARI) is(n)=my(k=n%20); (k==3||k==9||k==11) && isprime(2*n+1) && isprime(n) \\ Charles R Greathouse IV, Nov 20 2014

Crossrefs

Subset of A005384.

Cf. A000353.

Sequence in context: A289765 A141226 A049491 * A163769 A100860 A018630

Adjacent sequences: A000352 A000353 A000354 * A000356 A000357 A000358

Keyword

nonn,easy

Author

Robert A. J. Matthews

Extensions

More terms from Reinhard Zumkeller, Feb 10 2009

Status

approved