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A102986 Numbers n such that 4*10^n + 2*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
1, 4, 136, 181, 325, 3292, 3871, 4690, 7876, 11911, 16096, 21649, 43045 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers n such that (38*10^n+43)/9 is prime.

a(14) > 10^5. - Robert Price, May 08 2015

LINKS

Table of n, a(n) for n=1..13.

Makoto Kamada, Prime numbers of the form 422...227.

Index entries for primes involving repunits.

FORMULA

a(n) = A101721(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(38*10^n + 43)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101721.

Sequence in context: A263588 A006429 A016483 * A012160 A012197 A202299

Adjacent sequences:  A102983 A102984 A102985 * A102987 A102988 A102989

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 17 2005

EXTENSIONS

Addition of a(10)-a(12) from Kamada data by Robert Price, Dec 13 2010

a(13) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013

STATUS

approved

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Last modified December 7 05:14 EST 2019. Contains 329839 sequences. (Running on oeis4.)