

A000355


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


3



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
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OFFSET

1,1


COMMENTS

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


REFERENCES

R. A. J. Matthews, Maximally periodic reciprocals, Bull. Institute of Mathematics and Its Applications, vol. 28, p. 147148, 1992.


LINKS

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


PROG

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


CROSSREFS

Subset of A005384.
Sequence in context: A177789 A141226 A049491 * A163769 A100860 A018630
Adjacent sequences: A000352 A000353 A000354 * A000356 A000357 A000358


KEYWORD

nonn,easy


AUTHOR

R. A. J. Matthews [ 100265.3005(AT)compuserve.com ]


EXTENSIONS

More terms from Reinhard Zumkeller, Feb 10 2009


STATUS

approved



