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A056701 Numbers n such that 2*10^n + 3*R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
0, 1, 2, 3, 4, 10, 16, 22, 53, 91, 94, 106, 138, 210, 282, 522, 597, 1049, 2227, 6459, 10582, 18895, 41269, 50702, 53185, 59796 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Also numbers n such that (7*10^n-1)/3 is prime.

a(27) > 10^5. - Robert Price, Oct 19 2014

LINKS

Table of n, a(n) for n=1..26.

Makoto Kamada, Prime numbers of the form 233...33.

Index entries for primes involving repunits

MATHEMATICA

Do[ If[ PrimeQ[ 2*10^n + 3*(10^n-1)/9], Print[n]], {n, 0, 15001}]

CROSSREFS

Cf. A002275, A093672.

Sequence in context: A183527 A085934 A220402 * A285190 A055506 A098088

Adjacent sequences:  A056698 A056699 A056700 * A056702 A056703 A056704

KEYWORD

hard,nonn,more

AUTHOR

Robert G. Wilson v, Aug 10 2000

EXTENSIONS

a(22)-a(26) from Kamada data by Robert Price, Oct 19 2014

STATUS

approved

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Last modified April 21 01:03 EDT 2019. Contains 322310 sequences. (Running on oeis4.)