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A068497
Primes p such that 2*p+1 and 2*p-1 are composites.
6
13, 17, 43, 47, 59, 61, 67, 71, 73, 101, 103, 107, 109, 127, 137, 149, 151, 163, 167, 181, 193, 197, 223, 227, 241, 257, 263, 269, 277, 283, 311, 313, 317, 347, 349, 353, 373, 383, 389, 397, 401, 409, 421, 433, 449, 457, 461, 463, 467, 479, 487, 503, 521
OFFSET
1,1
COMMENTS
Subsequence of A053176. - Michel Marcus, Jan 12 2015
The sequence is infinite. Among others it contains all the primes of the form 15m+/-2. - Emmanuel Vantieghem, Sep 19 2016
LINKS
MAPLE
select(p->isprime(p) and not isprime(2*p+1) and not isprime(2*p-1), [$1..530]); # Muniru A Asiru, Oct 16 2018
MATHEMATICA
lst={}; Do[p=Prime[n]; If[ !PrimeQ[2*p-1]&&!PrimeQ[2*p+1], AppendTo[lst, p]], {n, 6!}]; lst (* Vladimir Joseph Stephan Orlovsky, May 12 2010 *)
Select[Prime[Range[500]], ! PrimeQ[2*# - 1] && ! PrimeQ[2*# + 1] &] (* G. C. Greubel, Oct 15 2018 *)
PROG
(PARI) listp(nn) = {forprime(p=2, nn, if (!isprime(2*p-1) && !isprime(2*p+1), print1(p, ", ")); ); } \\ Michel Marcus, Jan 12 2015
(Magma) [p: p in PrimesUpTo(600) | not IsPrime(2*p+1) and not IsPrime(2*p-1)]; // Vincenzo Librandi, Jan 20 2015
(GAP) Filtered([1..530], p->IsPrime(p) and not IsPrime(2*p+1) and not IsPrime(2*p-1)); # Muniru A Asiru, Oct 16 2018
CROSSREFS
Sequence in context: A043893 A279392 A239901 * A125524 A156553 A248474
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Mar 25 2002
STATUS
approved