A056706 - OEIS

This site is supported by donations to The OEIS Foundation.

A056706

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

1, 3, 13, 25, 72, 108, 375, 393, 589, 973 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	COMMENTS	`Also numbers n such that (37*10^n-1)/9 is prime.`
	LINKS	`Makoto Kamada, Factorizations of 411...11` `Index entries for primes involving repunits`
	MATHEMATICA	`Do[ If[ PrimeQ[ 4*10^n + (10^n-1)/9], Print[n]], {n, 0, 10000}]`
	CROSSREFS	`Sequence in context: A146379 A056714 A120074 * A052454 A066947 A031011` `Adjacent sequences: A056703 A056704 A056705 * A056707 A056708 A056709`
	KEYWORD	`hard,nonn`
	AUTHOR	`Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 10 2000`

Content is available under The OEIS End-User License Agreement .

Last modified February 15 11:21 EST 2012. Contains 205777 sequences.