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 A291202 Numbers k such that (43*10^k + 83)/9 is prime. 0
 2, 3, 8, 11, 17, 41, 57, 62, 77, 101, 329, 333, 359, 365, 968, 1169, 1190, 1772, 2237, 12075, 30848, 63200, 190547 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For k>1, numbers such that the digit 4 followed by k-2 occurrences of the digit 7 followed by the digits 87 is prime (see Example section). a(24) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 47w87. EXAMPLE 3 is in this sequence because (43*10^3 + 83)/9 = 4787 is prime. Initial terms and primes associated: a(1) = 2, 487; a(2) = 3, 4787; a(3) = 8, 477777787; a(4) = 11, 477777777787; a(5) = 17, 477777777777777787; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(43*10^# + 83)/9] &] PROG (MAGMA) [n: n in [1..300] |IsPrime((43*10^n + 83) div 9)]; // Vincenzo Librandi, Aug 21 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A212771 A119116 A138756 * A091076 A112595 A041075 Adjacent sequences:  A291199 A291200 A291201 * A291203 A291204 A291205 KEYWORD nonn,more,hard AUTHOR Robert Price, Aug 20 2017 EXTENSIONS a(23) from Robert Price, Nov 28 2018 STATUS approved

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Last modified March 26 22:42 EDT 2019. Contains 321565 sequences. (Running on oeis4.)