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 A098960 Numbers n such that 2*10^n + 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 2, 6, 33, 69, 150, 936, 3135, 5838, 6990, 20786, 57138 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also numbers n such that (25*10^n-61)/9 is prime. a(12) > 10^5. - Robert Price, Feb 27 2015 LINKS Makoto Kamada, Prime numbers of the form 277...771. FORMULA a(n) = A101966(n) + 1. EXAMPLE For n = 2 and 6, we get 271 and 2777771 which are primes. MATHEMATICA Do[ If[ PrimeQ[(25*10^n - 61)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101966. Sequence in context: A213435 A083666 A083126 * A162429 A279461 A243324 Adjacent sequences:  A098957 A098958 A098959 * A098961 A098962 A098963 KEYWORD more,nonn AUTHOR Julien Peter Benney (jpbenney(AT)ftml.net), Oct 22 2004 EXTENSIONS a(6) from Ray Chandler, Nov 04 2004 a(7), a(8) & a(9) from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 03 2004 Addition of a(10) from Kamada data by Robert Price, Dec 13 2010 a(11) from Robert Price, Feb 27 2015 STATUS approved

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Last modified July 27 14:43 EDT 2017. Contains 289866 sequences.