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 A293759 Numbers k such that (35*10^k - 197)/9 is prime. 0
 1, 2, 4, 7, 8, 19, 26, 28, 38, 43, 67, 331, 359, 832, 907, 1880, 2359, 4301, 5896, 6187, 37154, 40411, 59584 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k>1, numbers such that the digit 3 followed by k-2 occurrences of the digit 8 followed by the digits 67 is prime (see Example section). a(24) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 38w67 EXAMPLE 2 is in this sequence because (35*10^2 - 197)/9 = 367 is prime. Initial terms and primes associated: a(1) = 1, 17; a(2) = 2, 367; a(3) = 4, 38867; a(4) = 7, 38888867; a(5) = 8, 388888867; etc. MATHEMATICA Select[Range[1, 100000], PrimeQ[(35*10^# - 197)/9] &] PROG (MAGMA) [n: n in [1..400] |IsPrime((35*10^n - 197) div 9)]; // Vincenzo Librandi, Oct 16 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A045594 A013056 A013131 * A122979 A122980 A012985 Adjacent sequences:  A293756 A293757 A293758 * A293760 A293761 A293762 KEYWORD nonn,more,hard AUTHOR Robert Price, Oct 15 2017 EXTENSIONS Comments, Link and Example corrected by Robert Price, Jun 11 2018 STATUS approved

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Last modified May 12 04:27 EDT 2021. Contains 343810 sequences. (Running on oeis4.)