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 A103101 Numbers n such that 9*10^n + 5*R_n - 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 0, 2, 20, 104, 329, 1442, 1721, 24887 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (86*10^n-23)/9 is prime. a(9) > 10^5. - Robert Price, Nov 08 2015 LINKS Makoto Kamada, Prime numbers of the form 955...553. FORMULA a(n) = A101010(n-1) + 1, for n>1. MATHEMATICA Do[ If[ PrimeQ[(86*10^n - 23)/9], Print[n]], {n, 0, 10000}] PROG (PARI) for(n=0, 1e5, if(isprime((86*10^n-23)/9), print1(n, ", "))); \\ Altug Alkan, Nov 08 2015 CROSSREFS Cf. A002275, A101010. Sequence in context: A220856 A035599 A222556 * A267678 A009357 A052361 Adjacent sequences:  A103098 A103099 A103100 * A103102 A103103 A103104 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 19 2005 EXTENSIONS a(8) from Kamada data by Robert Price, Dec 14 2010 Inserted a(1)=0 by Robert Price, Nov 08 2015 STATUS approved

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Last modified August 7 09:16 EDT 2020. Contains 336274 sequences. (Running on oeis4.)