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URL: https://oeis.org/A102939

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A102939
Numbers k such that 10^k + 6*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
2
1, 2, 3, 18, 177, 324, 388, 392, 404, 531, 1083, 12546, 22443, 54388, 72916, 185520
OFFSET
1,2
COMMENTS
Also numbers k such that (5*10^k - 11)/3 is prime.
a(16) > 10^5. - Robert Price, Nov 15 2014
FORMULA
a(n) = A102023(n) + 1.
MAPLE
A102939:=n->`if`(isprime((5*10^n-11)/3), n, NULL): seq(A102939(n), n=1..1000); # Wesley Ivan Hurt, Nov 15 2014
MATHEMATICA
Do[ If[ PrimeQ[(5*10^n - 11)/3], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A226961 A374865 A107095 * A073983 A230602 A269343
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Dec 16 2004
EXTENSIONS
Addition of a(12)-a(13) from Kamada data by Robert Price, Dec 12 2010
a(14)-a(15) from Kamada data by Robert Price, Nov 15 2014
a(16) from Kamada data by Tyler Busby, Apr 16 2024
STATUS
approved