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 A056716 Numbers n such that 6*10^n-1 is prime. 4
 0, 1, 2, 4, 5, 7, 10, 13, 22, 23, 28, 34, 40, 61, 73, 361, 490, 613, 1624, 2000, 2994, 4301, 4332, 18668, 32544, 34936, 267598, 270658, 293134, 319889, 414508 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Also numbers n such that 5*10^n + 9*R_n is prime, where R_n = 11...1 is the repunit (A002275) of length n. LINKS Makoto Kamada, Prime numbers of the form 599...99. MATHEMATICA Do[ If[ PrimeQ[ 6*10^n - 1], Print[n]], {n, 0, 5000}] PROG (PARI) is(n)=ispseudoprime(6*10^n-1) \\ Charles R Greathouse IV, Feb 20 2017 CROSSREFS Cf. A056805 (6*10^n+1 is prime). Sequence in context: A211523 A340246 A062463 * A223729 A190235 A023181 Adjacent sequences:  A056713 A056714 A056715 * A056717 A056718 A056719 KEYWORD hard,nonn,more AUTHOR Robert G. Wilson v, Aug 11 2000 EXTENSIONS More terms from Hugo Pfoertner, Feb 12 2004 3 more terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 30 2007 a(27)-a(31) from Kamada data by Robert Price, Oct 19 2014 Outdated comment deleted by Harvey P. Dale, Mar 01 2020 STATUS approved

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Last modified August 7 23:50 EDT 2022. Contains 355995 sequences. (Running on oeis4.)