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A059453 Sophie Germain primes (A005384) which are not safe primes (A005385). 9
2, 3, 29, 41, 53, 89, 113, 131, 173, 191, 233, 239, 251, 281, 293, 419, 431, 443, 491, 509, 593, 641, 653, 659, 683, 743, 761, 809, 911, 953, 1013, 1031, 1049, 1103, 1223, 1229, 1289, 1409, 1451, 1481, 1499, 1511, 1559, 1583, 1601, 1733, 1811, 1889, 1901 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A156660(a(n))*(1-A156659(a(n))) = 1. - Reinhard Zumkeller, Feb 18 2009

LINKS

Table of n, a(n) for n=1..49.

C. K. Caldwell, Cunningham Chains

EXAMPLE

89 is here because (89-1)/2=44 is not prime, but 2*89 + 1 = 179 is prime. Except for 2 and 3 these primes are congruent to 5 or 11 modulo 12. Introducing terms of Cunningham chains of first kind.

MATHEMATICA

lst={}; Do[p=Prime[n]; If[ !PrimeQ[(p-1)/2], If[PrimeQ[2*p+1], AppendTo[lst, p]]], {n, 6!}]; lst (* Vladimir Joseph Stephan Orlovsky, Jun 24 2009 *)

Select[Prime[Range[300]], PrimeQ[2#+1]&&!PrimeQ[(#-1)/2]&] (* Harvey P. Dale, Nov 10 2017 *)

CROSSREFS

Cf. A005384, A005385, A053176, A059452-A059456, A007700, A005602, A023272, A023302, A023330.

Sequence in context: A284649 A141192 A215135 * A235481 A214889 A137472

Adjacent sequences:  A059450 A059451 A059452 * A059454 A059455 A059456

KEYWORD

nonn

AUTHOR

Labos Elemer, Feb 02 2001

STATUS

approved

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Last modified April 19 16:52 EDT 2019. Contains 322282 sequences. (Running on oeis4.)