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URL: https://oeis.org/A103090

⇱ A103090 - OEIS

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A103090
Numbers k such that 8*10^k + 7*R_k - 4 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
1
1, 7, 36, 99, 325, 1227, 9261, 9414, 11115, 25149, 43212, 95214
OFFSET
1,2
COMMENTS
Also numbers k such that (79*10^k - 43)/9 is prime.
FORMULA
a(n) = A101077(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(79*10^n - 43)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A018199 A063168 A163683 * A250414 A212141 A212088
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 19 2005
EXTENSIONS
a(9)-a(11) from Kamada data by Robert Price, Dec 14 2010
a(12) from Kamada data by Tyler Busby, May 03 2024
STATUS
approved