

A103053


Numbers n such that 7*10^n + 2*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


1



1, 4, 12, 13, 15, 36, 40, 90, 837, 2424, 2427, 2443, 15925, 16212
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OFFSET

1,2


COMMENTS

Also numbers n such that (65*10^n+7)/9 is prime.
a(15) > 10^5.  Robert Price, Sep 22 2015


LINKS

Table of n, a(n) for n=1..14.
Makoto Kamada, Prime numbers of the form 722...223.
Index entries for primes involving repunits.


FORMULA

a(n) = A101134(n) + 1.


MATHEMATICA

Do[ If[ PrimeQ[(65*10^n + 7)/9], Print[n]], {n, 0, 10000}]


CROSSREFS

Cf. A002275, A101134.
Sequence in context: A051434 A074138 A120252 * A087760 A237279 A032498
Adjacent sequences: A103050 A103051 A103052 * A103054 A103055 A103056


KEYWORD

more,nonn


AUTHOR

Robert G. Wilson v, Jan 19 2005


EXTENSIONS

a(13)a(14) from Kamada data by Robert Price, Dec 14 2010


STATUS

approved



