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 A102954 Numbers n such that 2*10^n + 4*R_n + 3 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 3, 9, 15, 21, 27, 87, 180, 1941, 3960, 4995, 8577, 23481, 27855, 80595 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also numbers n such that (22*10^n+23)/9 is prime. a(15) > 10^5. - Robert Price, Mar 15 2015 LINKS Makoto Kamada, Prime numbers of the form 244...447. FORMULA a(n) = A101959() + 1. MATHEMATICA Do[ If[ PrimeQ[(22*10^n + 23)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101959. Sequence in context: A222640 A110108 A162843 * A272749 A273560 A246388 Adjacent sequences:  A102951 A102952 A102953 * A102955 A102956 A102957 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 17 2004 EXTENSIONS Addition of a(12)-a(13) from Kamada data by Robert Price, Dec 12 2010 a(14) from Robert Price, Mar 15 2015 STATUS approved

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Last modified October 18 12:18 EDT 2019. Contains 328160 sequences. (Running on oeis4.)