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A102988 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. 1
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, 22048, 25713, 28644, 43353 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers n such that (13*10^n-7)/3 is prime.

a(30) > 10^5. - Robert Price, Mar 30 2015

LINKS

Table of n, a(n) for n=1..29.

Makoto Kamada, Prime numbers of the form 433...331.

Index entries for primes involving repunits.

FORMULA

a(n) = A101723(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(13*10^n - 7)/3], Print[n]], {n, 1, 10000}]

CROSSREFS

Cf. A002275, A101723.

Sequence in context: A007087 A101359 A007303 * A080137 A102933 A122019

Adjacent sequences:  A102985 A102986 A102987 * A102989 A102990 A102991

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 17 2005

EXTENSIONS

Addition of a(26)-a(28) from Kamada data by Robert Price, Dec 08 2010

a(29) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013

STATUS

approved

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Last modified October 18 08:08 EDT 2019. Contains 328146 sequences. (Running on oeis4.)