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A102962
Numbers n such that 2*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
3, 6, 18, 69, 443, 449, 455, 2459, 4745, 7973, 14249, 31710
OFFSET
1,1
COMMENTS
Also numbers n such that (26*10^n-17)/9 is prime.
a(13) > 10^5. - Robert Price, Mar 28 2015
FORMULA
a(n) = A101971(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(26*10^n - 17)/9], Print[n]], {n, 0, 10000}]
Select[Range[10000], PrimeQ[(26 10^# - 17) / 9] &] (* Vincenzo Librandi, Mar 29 2015 *)
PROG
(Magma) [n: n in [0..100] | IsPrime((26*10^n-17) div 9)]; // Vincenzo Librandi, Mar 29 2015
CROSSREFS
Sequence in context: A215635 A215634 A178789 * A076510 A220816 A038060
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Dec 17 2004
EXTENSIONS
Addition of a(11) from Kamada data by Robert Price, Dec 13 2010
a(12) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013
STATUS
approved