

A259122


Numbers k such that 5*R_k + 10^k  4 is prime, where R_k = 11...11 is the repunit (A002275) of length k.


0




OFFSET

1,2


COMMENTS

Also, numbers k such that (14*10^k  41)/9 is prime.
Terms from Kamada data.
a(10) > 10^5.


LINKS

Table of n, a(n) for n=1..9.
Makoto Kamada, Nearrepdigit numbers of the form ABB...BBA.
Makoto Kamada, Prime numbers of the form 155...551.
Index entries for primes involving repunits.


EXAMPLE

For k=4, 5*R_4 + 10^k  4 = 5555 + 10000  4 = 15551 which is prime.


MATHEMATICA

Select[Range[100000], PrimeQ[(14*10^#41)/9] &]


CROSSREFS

Cf. A002275.
Sequence in context: A201502 A069535 A108866 * A059206 A294230 A332626
Adjacent sequences: A259119 A259120 A259121 * A259123 A259124 A259125


KEYWORD

nonn,more,hard


AUTHOR

Robert Price, Jun 18 2015


STATUS

approved



