A099409 - OEIS

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A099409

Numbers n such that 2*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

1, 3, 9, 15, 28, 64, 1168, 1695, 2362 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,2`
	COMMENTS	`Also numbers n such that (2*10^n+43)/9 is prime.`
	LINKS	`Table of n, a(n) for n=1..9.` `Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[ 2(10^n - 1)/9 + 5], Print[n]], {n, 5000}]`
	CROSSREFS	`Sequence in context: A131801 A122819 A056287 * A002127 A061810 A048701` `Adjacent sequences: A099406 A099407 A099408 * A099410 A099411 A099412`
	KEYWORD	`nonn`
	AUTHOR	`Robert G. Wilson v, Oct 14 2004`
	STATUS	`approved`

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Last modified May 23 22:29 EDT 2013. Contains 225613 sequences.