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 A282139 Numbers k such that (22*10^k - 19)/3 is prime. 0
 1, 2, 4, 6, 14, 15, 24, 48, 78, 112, 122, 334, 504, 872, 914, 1230, 1506, 2442, 4095, 5022, 10615, 11460, 18303, 33675, 47701, 55592, 84159, 146661 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k > 1, numbers such that the digit 7 followed by k - 2 occurrences of the digit 3 followed by the digits 27 is prime (see Example section). a(29) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 73w27. EXAMPLE 4 is in this sequence because (22*10^4 - 19)/3 = 73327 is prime. Initial terms and primes associated: a(1) = 1, 67; a(2) = 2, 727; a(3) = 4, 73327; a(4) = 6, 7333327; a(5) = 14, 733333333333327; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(22 * 10^# - 19)/3] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A295618 A324376 A027712 * A138307 A323101 A124693 Adjacent sequences:  A282136 A282137 A282138 * A282140 A282141 A282142 KEYWORD nonn,more,hard AUTHOR Robert Price, Feb 06 2017 EXTENSIONS a(28) from Robert Price, Apr 27 2019 STATUS approved

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Last modified August 14 10:47 EDT 2020. Contains 336480 sequences. (Running on oeis4.)