

A099417


Numbers n such that 5*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


2



0, 1, 3, 4, 6, 10, 15, 22, 88, 207, 528, 960, 2100, 18522, 36783, 38517
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OFFSET

1,3


COMMENTS

Also numbers n such that (5*10^n+13)/9 is prime.
a(17) > 10^5.  Robert Price, Oct 18 2014


LINKS

Table of n, a(n) for n=1..16.
Makoto Kamada, Prime numbers of the form 55...557.
Index entries for primes involving repunits


FORMULA

a(n) = A056686(n1) + 1.


MATHEMATICA

Do[ If[ PrimeQ[ 5(10^n  1)/9 + 2], Print[n]], {n, 0, 5000}]


CROSSREFS

Cf. A002275, A056686.
Sequence in context: A125869 A059618 A114736 * A139463 A287067 A310004
Adjacent sequences: A099414 A099415 A099416 * A099418 A099419 A099420


KEYWORD

nonn


AUTHOR

Robert G. Wilson v, Oct 14 2004


EXTENSIONS

a(14)a(16) from Robert Price, Oct 18 2014


STATUS

approved



