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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, 278325
OFFSET
1,3
COMMENTS
For k > 0, 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(43) > 3*10^5.
EXAMPLE
6 is in this sequence because (266*10^n+1)/3 = 88666667 is prime.
Initial terms and associated primes:
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
Sequence in context: A086736 A175773 A234949 * A276642 A320317 A017846
KEYWORD
nonn,more
AUTHOR
Robert Price, Feb 22 2016
EXTENSIONS
a(39)-a(41) from Robert Price, Apr 22 2020
a(42) from Robert Price, May 31 2023
STATUS
approved