

A102959


Numbers n such that 2*10^n + 7*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


1



1, 4, 34, 36, 42, 52, 163, 208, 216, 1417, 14646, 22794, 25648, 32515, 51421
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OFFSET

1,2


COMMENTS

Also numbers n such that (25*10^n+11)/9 is prime.


LINKS



FORMULA



MATHEMATICA

Do[ If[ PrimeQ[(25*10^n + 11)/9], Print[n]], {n, 0, 10000}]


CROSSREFS



KEYWORD

more,nonn


AUTHOR



EXTENSIONS

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


STATUS

approved



