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 A102942 Numbers n such that 10^n + 7*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 1, 2, 8, 26, 44, 167, 185, 3818, 8741, 50795 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (16*10^n-43)/9 is prime. a(11) > 10^5. - Robert Price, Feb 11 2015 LINKS Makoto Kamada, Prime numbers of the form 177...773. FORMULA a(n) = A102027(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(16*10^n - 43)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A102027. Sequence in context: A150673 A242747 A195585 * A212691 A206803 A212527 Adjacent sequences:  A102939 A102940 A102941 * A102943 A102944 A102945 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 16 2004 EXTENSIONS a(10) from Robert Price, Feb 11 2015 STATUS approved

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Last modified December 9 16:42 EST 2019. Contains 329879 sequences. (Running on oeis4.)