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A056705 Numbers k such that 3*10^k + 7*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k. 1
0, 1, 11, 17, 773, 18155 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Also numbers k such that (34*10^k - 7)/9 is prime.
LINKS
MATHEMATICA
Do[ If[ PrimeQ[ 3*10^n + 7*(10^n-1)/9], Print[n]], {n, 0, 30070}]
CROSSREFS
Sequence in context: A228055 A132092 A226258 * A259744 A065706 A078874
KEYWORD
hard,nonn
AUTHOR
Robert G. Wilson v, Aug 10 2000
STATUS
approved

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Last modified June 13 22:21 EDT 2024. Contains 373391 sequences. (Running on oeis4.)