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A103023
Numbers n such that 5*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
2, 6, 8, 20, 108, 288, 306, 462, 20102, 30042, 69050
OFFSET
1,1
COMMENTS
Also numbers n such that (53*10^n-17)/9 is prime.
a(12) > 10^5. - Robert Price, Sep 07 2015
FORMULA
a(n) = A101588(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(53*10^n - 17)/9], Print[n]], {n, 0, 10000}]
Select[Range[0, 10000], PrimeQ[(53 10^# - 17)/9] &] (* Vincenzo Librandi, Sep 08 2015 *)
PROG
(Magma) [n: n in [0..350] | IsPrime((53*10^n-17) div 9)]; // Vincenzo Librandi, Sep 08 2015
CROSSREFS
Sequence in context: A290160 A290213 A058775 * A341732 A111247 A045656
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 18 2005
EXTENSIONS
Addition of a(9) from Kamada data by Robert Price, Dec 13 2010
a(10) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013
a(11) from Robert Price, Sep 07 2015
STATUS
approved