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 A102978 Numbers n such that 3*10^n + 8*R_n - 7 is a prime, where R_n = 11...1 is the repunit (A002275) of length n. 2
 1, 3, 19, 30, 40, 42, 45, 70, 307, 538, 1609, 1668, 1674, 4492, 4935, 6112, 12819, 14079, 16020, 23005, 50997, 82870 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (35*10^n-71)/9 is a prime. a(23) > 10^5. - Robert Price, May 20 2015 LINKS Makoto Kamada, Prime numbers of the form 388...881. FORMULA a(n) = A101844(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(35*10^n - 71)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101844. Sequence in context: A180451 A108137 A250027 * A218537 A236969 A222590 Adjacent sequences:  A102975 A102976 A102977 * A102979 A102980 A102981 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 17 2004 EXTENSIONS Addition of a(17)-a(20) from Kamada data by Robert Price, Dec 10 2010 a(21)-a(22) from Robert Price, May 20 2015 STATUS approved

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Last modified November 29 02:45 EST 2020. Contains 338756 sequences. (Running on oeis4.)