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A102968
Numbers n such that 3*10^n + 2*R_n + 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
3, 5, 9, 12, 27, 51, 53, 147, 155, 257, 519, 603, 2885, 9509, 10524, 19650, 32508, 79445, 158909
OFFSET
1,1
COMMENTS
Also numbers n such that (29*10^n+61)/9 is prime.
a(19) > 10^5. - Robert Price, Apr 05 2015
a(20) > 2*10^5. - Robert Price, Aug 12 2018
FORMULA
a(n) = A101831(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(29*10^n + 61)/9], Print[n]], {n, 0, 10000}]
Select[Range[10000], PrimeQ[(29 10^# + 61) / 9] &] (* Vincenzo Librandi, Apr 06 2015 *)
PROG
(Magma) [n: n in [0..500] | IsPrime((29*10^n + 61) div 9)]; // Vincenzo Librandi, Apr 06 2015
CROSSREFS
Sequence in context: A084593 A275843 A161866 * A180341 A348746 A177078
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Dec 17 2004
EXTENSIONS
A(13) from Julien Peter Benney (jpbenney(AT)ftml.net), Jan 16 2005
A(14) from Robert G. Wilson v, Jan 17 2005
Addition of a(15)-a(16) from Kamada data by Robert Price, Dec 12 2010
a(17) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013
a(18) from Robert Price, Apr 05 2015
a(19) from Robert Price, Aug 12 2018
STATUS
approved