

A102985


Numbers n such that 4*10^n + 2*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


1



0, 1, 4, 9, 10, 31, 70, 160, 171, 277, 630, 724, 3717, 5542, 5634, 10656, 12724, 31954
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OFFSET

1,3


COMMENTS

Also numbers n such that (38*10^n+7)/9 is prime.
a(19) > 10^5.  Robert Price, May 09 2015


LINKS

Table of n, a(n) for n=1..18.
Makoto Kamada, Prime numbers of the form 422...223.
Index entries for primes involving repunits.


FORMULA

a(n) = A101720(n1) + 1.


MATHEMATICA

Do[ If[ PrimeQ[(38*10^n + 7)/9], Print[n]], {n, 0, 10000}]


CROSSREFS

Cf. A002275, A101720.
Sequence in context: A141395 A121215 A178224 * A112401 A178360 A197125
Adjacent sequences: A102982 A102983 A102984 * A102986 A102987 A102988


KEYWORD

more,nonn


AUTHOR

Robert G. Wilson v, Jan 17 2005


EXTENSIONS

Addition of a(16)a(17) from Kamada data by Robert Price, Dec 12 2010
a(18) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013


STATUS

approved



