

A102953


Numbers k such that 2*10^k + 4*R_k  1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.


2



1, 4, 7, 12, 30, 94, 178, 196, 564, 1801, 3520, 3538, 8233, 35161, 37405, 42330, 70051, 90792, 124096, 152670
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OFFSET

1,2


COMMENTS

Also numbers k such that (22*10^k  13)/9 is prime.


LINKS



FORMULA



MATHEMATICA

Do[ If[ PrimeQ[(22*10^n  13)/9], Print[n]], {n, 0, 10000}]


CROSSREFS



KEYWORD

more,nonn


AUTHOR



EXTENSIONS

a(14)a(16) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013


STATUS

approved



