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 A269303 Numbers k such that (266*10^k + 1)/3 is prime. 504
 0, 1, 2, 3, 4, 5, 6, 8, 10, 13, 19, 26, 37, 69, 77, 81, 214, 242, 255, 900, 1113, 1833, 3166, 3566, 4753, 4849, 4869, 5005, 7372, 7702, 10240, 16100, 18972, 28574, 33815, 37820, 70457, 89482, 106066, 133603, 154897 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Numbers k such that digits 88 followed by k-1 occurrences of digit 6 followed by the digit 7 is prime (see Example section). a(42) > 2*10^5. LINKS Makoto Kamada, Search for 886w7. EXAMPLE 6 is in this sequence because (266*10^n+1)/3 = 88666667 is prime. Initial terms and primes associated: a(1)  = 0,    89; a(2)  = 1,    887; a(3)  = 2,    8867; a(4)  = 3,    88667; a(5)  = 4,    886667; a(6)  = 5,    8866667; a(7)  = 6,    88666667; a(8)  = 8,    8866666667; a(9)  = 10,   886666666667; a(10) = 13,   886666666666667, etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(266*10^#+1)/3] &] PROG (MAGMA) [n: n in [0..220] | IsPrime((266*10^n + 1) div 3)]; // Vincenzo Librandi, Feb 23 2016 (PARI) is(n)=ispseudoprime((266*10^n + 1)/3) \\ Charles R Greathouse IV, Feb 16 2017 CROSSREFS Cf. A056654, A268448. Sequence in context: A086736 A175773 A234949 * A276642 A320317 A017846 Adjacent sequences:  A269300 A269301 A269302 * A269304 A269305 A269306 KEYWORD nonn,more AUTHOR Robert Price, Feb 22 2016 EXTENSIONS a(38)-a(40) from Robert Price, Apr 22 2020 STATUS approved

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Last modified January 17 07:28 EST 2021. Contains 340214 sequences. (Running on oeis4.)