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A102975
Numbers n such that 3*10^n + 6*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
2
1, 2, 12, 15, 51, 194, 498, 2136, 2822, 3762, 7428, 22740, 30452, 37952, 55254
OFFSET
1,2
COMMENTS
Also numbers n such that (11*10^n+1)/3 is prime.
a(16) > 10^5. - Robert Price, Jan 29 2015
FORMULA
a(n) = A101840(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(11*10^n+1)/3], Print[n]], {n, 0, 10000}]
PROG
(Magma) [n: n in [0..300] | IsPrime((11*10^n+1) div 3)]; // Vincenzo Librandi, Dec 01 2015
CROSSREFS
Sequence in context: A077103 A036499 A107607 * A120300 A089021 A176888
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Dec 17 2004
EXTENSIONS
Addition of a(12) from Kamada data by Robert Price, Dec 13 2010
a(13)-a(14) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013
a(15) from Kamada data by Robert Price, Jan 29 2015
STATUS
approved