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A102971
Numbers n such that 3*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
1, 6, 9, 15, 24, 48, 73, 75, 97, 249, 273, 2488, 14499, 74773, 87448
OFFSET
1,2
COMMENTS
Also numbers n such that (32*10^n-41)/9 is prime.
a(16) > 10^5. - Robert Price, May 24 2015
FORMULA
a(n) = A101835(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(32*10^n-41)/9], Print[n]], {n, 0, 10000}]
Select[Range[0, 10000], PrimeQ[(32 10^# - 41)/9] &] (* Vincenzo Librandi, May 25 2015 *)
PROG
(Magma) [n: n in [0..2000] | IsPrime((32*10^n-41) div 9)]; // Vincenzo Librandi, May 25 2015
CROSSREFS
Sequence in context: A097426 A075278 A316048 * A023885 A031209 A271826
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Dec 17 2004
EXTENSIONS
Addition of a(13) from Kamada data by Robert Price, Dec 13 2010
a(14)-a(15) from Robert Price, May 24 2015
STATUS
approved