id:A056700 - OEIS Search Results

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Numbers n such that 2*10^n + R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n.

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2, 3, 12, 18, 23, 57, 128, 543, 584, 833, 2450, 2810, 2873, 3671, 6384 (list; graph; listen)

	OFFSET	`1,1`
	COMMENT	`Also numbers n such that (19*10^n-1)/9 is prime.`
	LINKS	`Makoto Kamada, Factorizations of 211...11` `Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[ 2*10^n + (10^n-1)/9], Print[n]], {n, 0, 10000}]`
	CROSSREFS	`Adjacent sequences: A056697 A056698 A056699 this_sequence A056701 A056702 A056703` `Sequence in context: A073452 A112976 A100570 this_sequence A140989 A130089 A126292`
	KEYWORD	`hard,nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 10 2000`
	EXTENSIONS	`6384 from Hugo Pfoertner (hugo(AT)pfoertner.org), Oct 16 2004`

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Last modified October 10 20:39 EDT 2008. Contains 144831 sequences.