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A102991 Numbers n such that 4*10^n + 5*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 2
0, 1, 4, 7, 19, 34, 54, 78, 90, 213, 307, 702, 1456, 2139, 2214, 3066, 9300, 16440, 16894, 28575, 54051 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Also numbers n such that (41*10^n-23)/9 is prime.

a(22) > 10^5. Robert Price, May 08 2015

LINKS

Table of n, a(n) for n=1..21.

Makoto Kamada, Prime numbers of the form 455...553.

Index entries for primes involving repunits.

FORMULA

a(n) = A101726(n-1) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(41*10^n - 23)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101726.

Sequence in context: A006381 A318099 A274691 * A298350 A291596 A323655

Adjacent sequences:  A102988 A102989 A102990 * A102992 A102993 A102994

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 17 2005

EXTENSIONS

Addition of a(17)-a(19) from Kamada data by Robert Price, Dec 10 2010

0 added by Arkadiusz Wesolowski, Mar 10 2011

A(21) from Robert Price, May 08 2015

STATUS

approved

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Last modified July 21 04:40 EDT 2019. Contains 325189 sequences. (Running on oeis4.)