

A103031


Numbers n such that 6*10^n + 2*R_n + 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


1




OFFSET

1,2


COMMENTS

Also numbers n such that (56*10^n+61)/9 is prime.
a(5) > 10^5.  Robert Price, Sep 07 2015


LINKS

Table of n, a(n) for n=1..4.
Makoto Kamada, Prime numbers of the form 622...229.
Index entries for primes involving repunits.


FORMULA

a(n) = A101524(n1) + 1 for n>1.


EXAMPLE

For n=0, (56*10^n+61)/9=13 which is prime, so 0 is in the sequence.


MATHEMATICA

Do[ If[ PrimeQ[(56*10^n + 61)/9], Print[n]], {n, 0, 10000}]


CROSSREFS

Cf. A002275, A101524.
Sequence in context: A036279 A156769 A029758 * A012474 A296940 A193119
Adjacent sequences: A103028 A103029 A103030 * A103032 A103033 A103034


KEYWORD

bref,more,nonn


AUTHOR

Robert G. Wilson v, Jan 18 2005


EXTENSIONS

Inserted a(1)=0 by Robert Price, Sep 07 2015


STATUS

approved



