

A056700


Numbers k such that 2*10^k + R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.


2



0, 2, 3, 12, 18, 23, 57, 128, 543, 584, 833, 2450, 2810, 2873, 3671, 6384, 10296, 16704, 53049, 56544, 74253
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OFFSET

1,2


COMMENTS

Also numbers k such that (19*10^k1)/9 is prime.


LINKS



MATHEMATICA

Do[ If[ PrimeQ[ 2*10^n + (10^n1)/9], Print[n]], {n, 0, 10000}]


CROSSREFS



KEYWORD

nonn,hard,more


AUTHOR



EXTENSIONS

10296 and 16704 from Ray Chandler, Sep 2010
53049 and 56544 from Serge Batalov, Mar 2009 confirmed as next terms by Ray Chandler, Feb 03 2012


STATUS

approved



