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 A103074 Numbers n such that 8*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 0, 2, 3, 5, 17, 47, 177, 8462, 36615 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (74*10^n-11)/9 is prime. a(10) > 10^5. - Robert Price, Oct 13 2015 LINKS Makoto Kamada, Prime numbers of the form 822...221. FORMULA a(n) = A101061(n-1) + 1 for n>1. MATHEMATICA Do[ If[ PrimeQ[(74*10^n - 11)/9], Print[n]], {n, 0, 10000}] PROG (PARI) for(n=0, 50000, if(isprime((74*10^n-11)/9), print1(n", "))) \\ Altug Alkan, Oct 13 2015 CROSSREFS Cf. A002275, A101061. Sequence in context: A235630 A235636 A268130 * A173236 A268209 A245641 Adjacent sequences:  A103071 A103072 A103073 * A103075 A103076 A103077 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 19 2005 EXTENSIONS a(9) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013 Inserted a(1)=0 by Robert Price, Oct 13 2015 STATUS approved

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