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A130771 Numbers n not divisible by 3 for which neither 2n-3 nor 2n+3 are primes. 1
26, 44, 59, 61, 79, 86, 103, 106, 109, 125, 128, 131, 146, 149, 151, 161, 163, 166, 169, 179, 184, 187, 194, 205, 224, 236, 239, 254, 257, 265, 266, 268, 271, 274, 278, 281, 289, 293, 296, 304, 313, 316, 326, 334, 341, 346, 350, 355, 359, 364, 367, 376, 389, 391 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
This is A130699 with the trivial multiples of 3 removed.
LINKS
EXAMPLE
26 because 2*26+3=55 is not a prime, nor is 2*26-3=49.
MATHEMATICA
Select[Range[400], !Divisible[#, 3]&&NoneTrue[2#+{3, -3}, PrimeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Sep 19 2018 *)
PROG
(PARI) isok(n) = (n % 3) && !isprime(2*n-3) && !isprime(2*n+3) \\ Michel Marcus, Jul 11 2013
CROSSREFS
Sequence in context: A248404 A280645 A260207 * A217775 A260200 A178100
KEYWORD
easy,nonn
AUTHOR
W. Neville Holmes, Jul 14 2007
EXTENSIONS
Missing term 169 added by Michel Marcus, Jul 11 2013
STATUS
approved

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Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)