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 A102740 Numbers k such that 7*10^k - 11 is prime. 0
 1, 6, 7, 9, 10, 11, 16, 42, 53, 78, 321, 699, 1858, 3425, 4899, 5734, 11081, 11675, 12136, 14056, 16074, 77969, 158465 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(24) > 2*10^5. Numbers corresponding to terms <= 699 are certified primes. - Klaus Brockhaus, Feb 15 2005 For k>1, numbers such that the digit 6 followed by k-2 occurrences of the digit 9 followed by the digits 89 is prime (see Example section). LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 69w89. EXAMPLE Initial terms and primes associated: a(1) = 1, 59; a(2) = 6, 6999989; a(3) = 7, 69999989; a(4) = 9, 6999999989; a(5) = 10, 69999999989; etc. MATHEMATICA Select[Range[1, 100000], PrimeQ[7*10^# - 11] &] PROG (PARI) is(n)=ispseudoprime(7*10^n - 11) \\ Charles R Greathouse IV, Jun 13 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A094868 A131956 A205720 * A248178 A284094 A120183 Adjacent sequences:  A102737 A102738 A102739 * A102741 A102742 A102743 KEYWORD more,nonn AUTHOR Tom Mueller (muel4503(AT)uni-trier.de), Feb 08 2005 EXTENSIONS a(11)-a(13) from Klaus Brockhaus, Feb 15 2005 a(14)-a(22) from Robert Price, Oct 29 2017 a(23) from Robert Price, Jun 21 2019 STATUS approved

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Last modified September 23 16:41 EDT 2020. Contains 337315 sequences. (Running on oeis4.)