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A103055 Numbers n such that 7*10^n + 3*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
1, 3, 4, 5, 6, 9, 12, 31, 59, 69, 74, 287, 489, 592, 634, 1089, 1607, 3141, 5962, 6267, 9678, 11431, 12927, 32189, 38700, 53033, 83525 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also numbers n such that (22*10^n-7)/3 is prime.

LINKS

Table of n, a(n) for n=1..27.

Makoto Kamada, Prime numbers of the form 733...331.

Index entries for primes involving repunits.

FORMULA

a(n) = A101137(n) + 1.

MATHEMATICA

Do[ If[ PrimeQ[(22*10^n - 7)/3], Print[n]], {n, 0, 10000}]

CROSSREFS

Cf. A002275, A101137.

Sequence in context: A088875 A022884 A105857 * A128995 A293306 A014101

Adjacent sequences:  A103052 A103053 A103054 * A103056 A103057 A103058

KEYWORD

more,nonn

AUTHOR

Robert G. Wilson v, Jan 19 2005

EXTENSIONS

a(22)-a(23) Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(24)-a(25) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013

a(26)-a(27) from Erik Branger Sep 08 2014 by Ray Chandler, Apr 23 2015

STATUS

approved

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Last modified October 22 07:06 EDT 2021. Contains 348160 sequences. (Running on oeis4.)