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 A056717 Numbers n such that 6*10^n + R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n. 1
 1, 5, 7, 25, 31, 112, 199, 533, 616, 718, 787, 1357, 2779, 3889, 4192, 7537, 7945, 23938, 32632, 49169, 56453, 61097, 90211 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers n such that (55*10^n-1)/9 is prime. LINKS Makoto Kamada, Prime numbers of the form 611...11. MATHEMATICA Do[ If[ PrimeQ[ 6*10^n + (10^n-1)/9], Print[n]], {n, 0, 10000}] CROSSREFS Cf. A002275, A093631. Sequence in context: A298900 A166660 A037374 * A072370 A057490 A057253 Adjacent sequences:  A056714 A056715 A056716 * A056718 A056719 A056720 KEYWORD nonn AUTHOR Robert G. Wilson v, Aug 11 2000 EXTENSIONS 2779,3889,4192,7537,7945 from Hugo Pfoertner, Oct 19 2004 23938 from Ray Chandler, Sep 25 2010 32632 and 49169 from Ray Chandler, Feb 08 2012 56453 from Serge Batalov, Mar 12 2009 confirmed as next term by Ray Chandler, Feb 09 2012 61097 from Ray Chandler, Feb 09 2012 90211 from Ray Chandler, Feb 10 2012 STATUS approved

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Last modified April 20 09:59 EDT 2019. Contains 322309 sequences. (Running on oeis4.)