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 A103099 Numbers n such that 9*10^n + 4*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 1, 2, 4, 25, 58, 148, 373, 421, 1915, 3746, 16784, 30050, 60026, 93346 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (85*10^n+23)/9 is prime. a(15) > 10^5. - Robert Price, Nov 14 2015 LINKS Makoto Kamada, Prime numbers of the form 944...447. FORMULA a(n) = A101008(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(85*10^n + 23)/9], Print[n]], {n, 0, 10000}] PROG (PARI) is(n)=isprime(9*10^n + 4*(10^n-1)/9 + 3) \\ Anders Hellström, Nov 14 2015 CROSSREFS Cf. A002275, A101008. Sequence in context: A128299 A143672 A001510 * A342665 A266495 A119029 Adjacent sequences: A103096 A103097 A103098 * A103100 A103101 A103102 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Jan 19 2005 EXTENSIONS a(11) from Kamada data by Robert Price, Dec 14 2010 a(12) from Erik Branger May 01 2013 by Ray Chandler, Aug 17 2013 a(13)-a(14) from Robert Price, Nov 14 2015 STATUS approved

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Last modified January 29 04:47 EST 2023. Contains 359915 sequences. (Running on oeis4.)