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A102929
Numbers k such that 10^k + 2*R_k + 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
1
0, 1, 3, 9, 48, 58, 153, 261, 876, 1179, 1596, 17715, 63718
OFFSET
1,3
COMMENTS
Also numbers k such that (11*10^k + 7)/9 is prime.
a(14) > 10^5. - Robert Price, Nov 15 2014
a(14) > 2*10^5. - Tyler Busby, Feb 01 2023
FORMULA
a(n) = A102009(n-1) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(11*10^n + 7)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A129432 A111551 A258481 * A105458 A366485 A306947
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Dec 16 2004
EXTENSIONS
Addition of a(12) from Kamada data by Robert Price, Dec 13 2010
Inserted a(1)=0 by Robert Price, Nov 15 2014
a(13) from Kamada data by Robert Price, Nov 15 2014
STATUS
approved