

A056713


Numbers k such that 5*10^k + R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.


1



0, 5, 12, 15, 84, 144, 150, 1235, 1727, 1812, 8687, 12390, 28608, 42959, 51111, 96798, 99143
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OFFSET

1,2


COMMENTS

Also numbers k such that (46*10^k  1)/9 is prime.
a(18) > 10^5.  Robert Price, Dec 08 2014


LINKS

Table of n, a(n) for n=1..17.
Makoto Kamada, Prime numbers of the form 511...11.
Index entries for primes involving repunits


MATHEMATICA

Do[ If[ PrimeQ[ 5*10^n + (10^n1)/9], Print[n]], {n, 0, 10000}]


CROSSREFS

Cf. A002275, A068816.
Sequence in context: A184399 A314275 A314276 * A110670 A111523 A078231
Adjacent sequences: A056710 A056711 A056712 * A056714 A056715 A056716


KEYWORD

hard,nonn


AUTHOR

Robert G. Wilson v, Aug 11 2000


EXTENSIONS

a(11) from Hugo Pfoertner, Oct 19 2004
a(12)a(17) from Robert Price, Dec 08 2014


STATUS

approved



