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A103014
Numbers n such that 5*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
1, 3, 4, 9, 12, 60, 268, 289, 384, 795, 3474, 9180, 76438
OFFSET
1,2
COMMENTS
Also numbers n such that (49*10^n-13)/9 is prime.
a(14) > 10^5. - Robert Price, Jul 16 2015
FORMULA
a(n) = A101579(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(49*10^n - 13)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A376684 A029448 A249179 * A116552 A339996 A225288
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 18 2005
EXTENSIONS
a(13) from Robert Price, Jul 16 2015
STATUS
approved