

A256906


Numbers k such that 7*R_k + 10 is prime, where R_k = 11...1 is the repunit (A002275) of length k.


0



1, 3, 6, 15, 21, 24, 31, 291, 408, 457, 643, 2671, 2676, 10893, 21151, 26445, 77304, 96312
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OFFSET

1,2


COMMENTS

Also, numbers k such that (7*10^k + 83)/9 is prime.
Terms from Kamada. Note Kamada does not recognize k=1 as 17 is a degenerate case of form AAA..ABA.
a(17) > 30000.


LINKS



EXAMPLE

For k=3, 7*R_11 + 10 = 777 + 10 = 787 which is prime.


MATHEMATICA

Select[Range[0, 30000], PrimeQ[(7*10^# + 83)/9] &]


CROSSREFS



KEYWORD

more,hard,nonn


AUTHOR



EXTENSIONS



STATUS

approved



