

A102947


Numbers n such that 2*10^n3 is prime.


2



1, 2, 3, 4, 13, 14, 76, 237, 872, 988, 1280, 1370, 2686, 3612, 4051, 4645, 9162, 10856, 25959, 64882, 144220, 153746, 185930
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OFFSET

1,2


COMMENTS

Numbers n such that 10^n + 8*R_n  2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
a(21) > 10^5.  Robert Price, Nov 16 2014
a(24) > 2*10^5.  Robert Price, Jul 11 2015


LINKS

Table of n, a(n) for n=1..23.
Makoto Kamada, Prime numbers of the form 199...997.
Index entries for primes involving repunits.


FORMULA

a(n) = A102034(n) + 1.


MATHEMATICA

Do[ If[ PrimeQ[2*10^n  3], Print[n]], {n, 0, 10000}]


PROG

(PARI) is(n)=ispseudoprime(2*10^n3) \\ Charles R Greathouse IV, Jun 06 2017


CROSSREFS

Cf. A102034.
Sequence in context: A303385 A325709 A126129 * A281512 A295396 A236440
Adjacent sequences: A102944 A102945 A102946 * A102948 A102949 A102950


KEYWORD

more,nonn


AUTHOR

Robert G. Wilson v, Dec 16 2004


EXTENSIONS

Addition of a(18)a(20) from Kamada data by Robert Price, Dec 09 2010
a(21)a(23) from Robert Price, Jul 11 2015


STATUS

approved



