|
| |
|
|
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
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
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. 147-148, 1992.
|
|
|
LINKS
|
R. Zumkeller, Table of n, a(n) for n = 1..1000
|
|
|
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
|
R. A. J. Matthews [ 100265.3005(AT)compuserve.com ]
|
|
|
EXTENSIONS
|
More terms from Reinhard Zumkeller, Feb 10 2009
|
|
|
STATUS
|
approved
|
| |
|
|
