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 A102956 Numbers n such that 2*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 1, 82, 322, 733, 2431, 8386, 15886, 19912 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (23*10^n+31)/9 is prime. a(9) > 10^5. - Robert Price, Feb 06 2015 LINKS Makoto Kamada, Prime numbers of the form 255...559. FORMULA a(n) = A101963(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(23*10^n + 31)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101963. Sequence in context: A227704 A248405 A116341 * A031696 A005972 A082972 Adjacent sequences:  A102953 A102954 A102955 * A102957 A102958 A102959 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 17 2004 EXTENSIONS Addition of a(7)-a(8) from Kamada data by Robert Price, Dec 13 2010 STATUS approved

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Last modified May 21 08:44 EDT 2022. Contains 353908 sequences. (Running on oeis4.)