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 A099006 Numbers n such that 2*10^n + 5*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 2, 3, 26, 27, 45, 62, 147, 1277, 1665, 1979, 2970, 12773, 17702, 19128, 22206, 22386, 25053 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also numbers n such that (23*10^n+13)/9 is prime. a(18) > 10^5. - Robert Price, Feb 16 2015 LINKS Makoto Kamada, Prime numbers of the form 255...557. FORMULA a(n) = A101962(n) + 1. EXAMPLE n = 2, 3, 26, 27 are members since 257, 2557, 255555555555555555555555557 and 2555555555555555555555555557 are primes. MATHEMATICA Do[ If[ PrimeQ[(23*10^n + 13)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101962. Sequence in context: A002748 A056004 A032812 * A041659 A042043 A178196 Adjacent sequences:  A099003 A099004 A099005 * A099007 A099008 A099009 KEYWORD more,nonn AUTHOR Julien Peter Benney (jpbenney(AT)ftml.net), Nov 07 2004 EXTENSIONS a(8), a(9), a(10) & a(11) from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 17 2004 a(12)-a(17) from Kamada data by Robert Price, Dec 14 2010 STATUS approved

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Last modified September 20 09:13 EDT 2020. Contains 337264 sequences. (Running on oeis4.)