

A102985


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


1



0, 1, 4, 9, 10, 31, 70, 160, 171, 277, 630, 724, 3717, 5542, 5634, 10656, 12724, 31954
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OFFSET

1,3


COMMENTS

Also numbers n such that (38*10^n+7)/9 is prime.


LINKS



FORMULA



MATHEMATICA

Do[ If[ PrimeQ[(38*10^n + 7)/9], Print[n]], {n, 0, 10000}]


CROSSREFS



KEYWORD

more,nonn


AUTHOR



EXTENSIONS

Addition of a(16)a(17) from Kamada data by Robert Price, Dec 12 2010
a(18) from Erik Branger, May 01 2013, submitted by Ray Chandler, Aug 16 2013


STATUS

approved



