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A102942
Numbers k such that 10^k + 7*R_k - 4 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
1
1, 2, 8, 26, 44, 167, 185, 3818, 8741, 50795
OFFSET
1,2
COMMENTS
Also numbers k such that (16*10^k - 43)/9 is prime.
a(11) > 10^5. - Robert Price, Feb 11 2015
FORMULA
a(n) = A102027(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(16*10^n - 43)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A150673 A242747 A195585 * A212691 A206803 A212527
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Dec 16 2004
EXTENSIONS
a(10) from Robert Price, Feb 11 2015
STATUS
approved