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 A294916 Numbers k such that (10^k + 191)/3 is prime. 0
 1, 2, 3, 6, 7, 13, 18, 33, 39, 126, 154, 168, 213, 4150, 4153, 5658, 6394, 21993, 29674, 38936, 47095, 94096, 135174, 139398 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k > 1, numbers such that k-2 occurrences of the digit 3 followed by the digits 97 is prime (see Example section). a(25) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 3w97 EXAMPLE 2 is in this sequence because (10^2 + 191)/3 = 97 is prime. Initial terms and primes associated: a(1) = 1, 67; a(2) = 2, 97; a(3) = 3, 397; a(4) = 6, 333397; a(5) = 7, 3333397; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(10^# + 191)/3] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A304709 A183558 A328164 * A233423 A328024 A309815 Adjacent sequences:  A294913 A294914 A294915 * A294917 A294918 A294919 KEYWORD nonn,more,hard AUTHOR Robert Price, Nov 10 2017 EXTENSIONS a(23)-a(24) from Robert Price, Feb 14 2018 STATUS approved

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Last modified January 27 14:39 EST 2020. Contains 331295 sequences. (Running on oeis4.)