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A163769
Primes p such that 2*p+3 is not prime.
4
3, 11, 23, 31, 37, 41, 59, 61, 71, 79, 83, 101, 103, 107, 109, 131, 149, 151, 163, 179, 181, 191, 211, 233, 239, 241, 251, 257, 263, 271, 281, 293, 311, 313, 317, 331, 347, 359, 367, 373, 389, 401, 419, 421, 431, 433, 443, 449, 457, 461, 479, 491, 499, 521
OFFSET
1,1
COMMENTS
All those p appear in A144562. [Proof: since 2p+3 is odd and not prime, it can be written as a product of two odd numbers, 2p+3=(2k+1)*(2s+1), therefore p=2ks+k+s-1. - R. J. Mathar, Aug 06 2009]
LINKS
FORMULA
A153238 INTERSECT A000040. - R. J. Mathar, Aug 05 2009
A000040 \ A023204. - R. J. Mathar, Aug 05 2009
EXAMPLE
3 is in the sequence because 2*3+3=9 is composite; 23 is in the sequence because 2*23+3=49 is composite.
MATHEMATICA
Select[Prime[Range[200]], !PrimeQ[2#+3]&] (* Harvey P. Dale, Feb 02 2012 *)
PROG
(Magma) [p: p in PrimesUpTo(700) | not IsPrime(2*p+3)]; // Vincenzo Librandi, Apr 08 2013
CROSSREFS
Cf. A144562.
Sequence in context: A141226 A049491 A000355 * A100860 A018630 A163780
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Aug 04 2009
EXTENSIONS
Entries checked - R. J. Mathar, Aug 06 2009
STATUS
approved