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 A280272 Numbers n such that (229*10^n - 1)/3 is prime. 0
 3, 6, 8, 9, 10, 17, 27, 28, 45, 81, 83, 225, 246, 1732, 2957, 3021, 5459, 5702, 5740, 7924, 15110, 18683, 25149, 46968, 48944, 49571, 70122, 147699, 158339 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers such that the digits 76 followed by n occurrences of the digit 3 is prime (see Example section). a(30) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 763w. EXAMPLE 3 is in this sequence because (229*10^3 - 1)/3 = 76333 is prime. Initial terms and primes associated: a(1) = 3, 76333; a(2) = 6, 76333333; a(3) = 8, 7633333333; a(4) = 9, 76333333333; a(5) = 10, 763333333333; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(229*10^# - 1)/3] &] PROG (PARI) is(n)=ispseudoprime((229*10^n - 1)/3) \\ Charles R Greathouse IV, Jun 13 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A201817 A299240 A004715 * A190234 A036558 A005870 Adjacent sequences:  A280269 A280270 A280271 * A280273 A280274 A280275 KEYWORD nonn,more,hard AUTHOR Robert Price, Dec 30 2016 EXTENSIONS a(24)-a(29) from Robert Price, Jul 10 2020 STATUS approved

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Last modified May 6 19:52 EDT 2021. Contains 343586 sequences. (Running on oeis4.)