id:A102988 - OEIS Search Results

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Numbers n such that 4*10^n + 3*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

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1, 2, 4, 7, 10, 12, 20, 24, 30, 42, 62, 188, 304, 340, 715, 804, 1040, 1887, 2079, 2120, 2260, 2423, 3319, 5598, 6072 (list; graph; listen)

	OFFSET	`1,2`
	COMMENT	`Also numbers n such that (13*10^n-7)/3 is prime.`
	LINKS	`Makoto Kamada, Factorizations of 433...331.` `Index entries for primes involving repunits.`
	MATHEMATICA	`Do[ If[ PrimeQ[(13*10^n - 7)/3], Print[n]], {n, 1, 10000}]`
	CROSSREFS	`Sequence in context: A007087 A101359 A007303 this_sequence A080137 A102933 A122019` `Adjacent sequences: A102985 A102986 A102987 this_sequence A102989 A102990 A102991`
	KEYWORD	`more,nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Jan 17 2005`

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Last modified February 9 11:24 EST 2010. Contains 172296 sequences.