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A103060 Numbers n such that 7*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
1, 2, 5, 7, 23, 32, 38, 47, 116, 140, 229, 247, 734, 931, 1346, 2162, 2546, 6980, 10283, 10543, 12128, 13741, 105320 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers n such that (68*10^n-41)/9 is prime.

LINKS

Table of n, a(n) for n=1..23.

Makoto Kamada, Prime numbers of the form 755...551.

Index entries for primes involving repunits.

FORMULA

a(n) = A101143(n) + 1. - Robert Price, Oct 13 2013

MATHEMATICA

Do[ If[ PrimeQ[(68*10^n - 41)/9], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A000533, A002275, A101143.

Sequence in context: A243394 A175552 A279756 * A256247 A243595 A103807

Adjacent sequences:  A103057 A103058 A103059 * A103061 A103062 A103063

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 19 2005

EXTENSIONS

a(19)-a(22) from Kamada data by Robert Price, Dec 14 2010

a(23) from Robert Price, Oct 13 2013

STATUS

approved

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Last modified April 14 05:00 EDT 2021. Contains 342941 sequences. (Running on oeis4.)