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A103064
Numbers n such that 7*10^n + 6*R_n - 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
1, 7, 90, 93, 125, 147, 498, 868, 879, 1157, 2958, 3018, 3317, 3822, 6948, 8885, 13092, 33323, 35847, 79492
OFFSET
1,2
COMMENTS
Also numbers n such that (23*10^n-11)/3 is prime.
a(21) > 10^5. - Robert Price, Oct 14 2015
FORMULA
a(n) = A101148(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(23*10^n - 11)/3], Print[n]], {n, 0, 10000}]
PROG
(Magma) [n: n in [0..500] | IsPrime((23*10^n-11) div 3)]; // Vincenzo Librandi, Oct 15 2015
CROSSREFS
Sequence in context: A142995 A350937 A200832 * A244849 A355591 A360914
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 19 2005
EXTENSIONS
a(17) from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(18)-a(19) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013
a(20) from Robert Price, Oct 14 2015
STATUS
approved