

A259130


Numbers k such that 4*R_k + 3*10^k  1 is prime, where R_k = 11...11 is the repunit (A002275) of length k.


0




OFFSET

1,2


COMMENTS

Also, numbers k such that (31*10^n13)/9 is prime.
Terms from Kamada data.
Note Kamada does not recognize k=0 as 2 is a degenerate case of form ABB..BBA.
a(7) > 2*10^5.


LINKS

Table of n, a(n) for n=1..6.
Makoto Kamada, Nearrepdigit numbers of the form ABB...BBA.
Makoto Kamada, Prime numbers of the form 344...443.
Index entries for primes involving repunits.


EXAMPLE

For k=6, 4*R_6 + 3*10^k  1 = 444444 + 3000000  1 = 3444443 which is prime.


MATHEMATICA

Select[Range[0, 100000], PrimeQ[(31*10^#13)/9] &]


CROSSREFS

Cf. A002275.
Sequence in context: A097174 A325030 A191415 * A032511 A036900 A159282
Adjacent sequences: A259127 A259128 A259129 * A259131 A259132 A259133


KEYWORD

nonn,more,hard


AUTHOR

Robert Price, Jun 18 2015


STATUS

approved



