id:A104279 - OEIS Search Results

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Numbers n such that 2n+1 is prime and 2n-1 is not prime.

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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; listen)

	OFFSET	`1,2`
	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`
	MATHEMATICA	`Select[ Range[218], PrimeQ[2# + 1] && !PrimeQ[2# - 1] &] (from Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 18 2005)`
	CROSSREFS	`Cf. A040040 and others.` `Sequence in context: A161537 A022798 A022808 this_sequence A063247 A118520 A001954` `Adjacent sequences: A104276 A104277 A104278 this_sequence A104280 A104281 A104282`
	KEYWORD	`easy,nonn`
	AUTHOR	`Alexandre Wajnberg (alexandre.wajnberg(AT)ulb.ac.be), Apr 17 2005`
	EXTENSIONS	`More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 18 2005`

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.

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