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 A102948 Numbers n such that 2*10^n + R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 1, 3, 7, 13, 24, 30, 48, 52, 163, 175, 219, 228, 261, 754, 951, 1344, 1573, 3294, 3523, 14161, 70794 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (19*10^n+17)/9 is prime. a(22) > 10^5. - Robert Price, Mar 04 2015 LINKS Makoto Kamada, Prime numbers of the form 211...113. FORMULA a(n) = A101953(n) + 1. MATHEMATICA Do[ If[ PrimeQ[(19*10^n + 17)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A101953. Sequence in context: A147380 A146606 A101302 * A232533 A061263 A156209 Adjacent sequences:  A102945 A102946 A102947 * A102949 A102950 A102951 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Dec 17 2004 EXTENSIONS Addition of a(20) from Kamada data by Robert Price, Dec 09 2010 a(21) from Robert Price, Mar 04 2015 STATUS approved

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Last modified April 6 21:24 EDT 2020. Contains 333286 sequences. (Running on oeis4.)