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 A103035 Numbers n such that 6*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 0, 2, 5, 6, 11, 15, 69, 90, 134, 189, 245, 267, 270, 470, 1575, 2295, 2507, 3512, 3825, 6857, 11022, 11657, 17499, 35036, 41966, 50558, 93062 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (58*10^n-13)/9 is prime. a(28) > 10^5. - Robert Price, Sep 12 2015 LINKS Makoto Kamada, Prime numbers of the form 644...443. FORMULA a(n) = A101528(n-1) + 1 for n>1. MATHEMATICA Do[ If[ PrimeQ[(58*10^n - 13)/9], Print[n]], {n, 0, 10000}] PROG (PARI) is(n)=isprime(6*10^n + 4*(10^n-1)/9 - 1) \\ Anders HellstrÃ¶m, Sep 12 2015 CROSSREFS Cf. A002275, A101528. Sequence in context: A336527 A293398 A180323 * A088273 A049054 A319140 Adjacent sequences:  A103032 A103033 A103034 * A103036 A103037 A103038 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 18 2005 EXTENSIONS a(21)-a(23) from Kamada data by Robert Price, Dec 14 2010 a(24)-a(25) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013 Inserted a(1)=0 by Robert Price, Sep 12 2015 a(26)-a(27) from Robert Price, Sep 12 2015 STATUS approved

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Last modified April 15 07:40 EDT 2021. Contains 342975 sequences. (Running on oeis4.)