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A104279
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Numbers n such that 2n+1 is prime and 2n-1 is not prime.
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1
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1, 5, 8, 11, 14, 18, 20, 23, 26, 29, 33, 35, 39, 41, 44, 48, 50, 53, 56, 63, 65, 68, 74, 78, 81, 83, 86, 89, 95, 98, 105, 111, 113, 116, 119, 125, 128, 131, 134, 138, 140, 146, 153, 155, 158, 165, 168, 173, 176, 179, 183, 186, 189, 191, 194, 198, 200, 204, 209, 215
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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EXAMPLE
| a(1)=1 because 3 is prime and 1 is not prime
a(2)=5 because 11 is prime and 9 is not prime
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MATHEMATICA
| Select[ Range[218], PrimeQ[2# + 1] && !PrimeQ[2# - 1] &] (from Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 18 2005)
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PROG
| (MAGMA) [n: n in [1..220]| not IsPrime(2*n-1) and IsPrime(2*n+1)] [From Vincenzo Librandi, Jan 28 2011]
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CROSSREFS
| Cf. A040040 and others.
Sequence in context: A180486 A022798 A022808 * A184919 A063247 A184928
Adjacent sequences: A104276 A104277 A104278 * A104280 A104281 A104282
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KEYWORD
| easy,nonn
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AUTHOR
| Alexandre Wajnberg (alexandre.wajnberg(AT)ulb.ac.be), Apr 17 2005
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 18 2005
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