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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

Table of n, a(n) for n=1..41.

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 May 24 19:08 EDT 2020. Contains 334580 sequences. (Running on oeis4.)