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A293531 Numbers k such that (268*10^k - 1)/3 is prime. 0
0, 2, 6, 7, 12, 13, 17, 18, 26, 77, 151, 222, 403, 567, 1107, 7221, 7722, 8475, 9729, 17904, 21404, 30170, 62523 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers such that the digits 89 followed by k occurrences of the digit 3 is prime (see Example section).

a(24) > 10^5.

LINKS

Table of n, a(n) for n=1..23.

Makoto Kamada, Factorization of near-repdigit-related numbers.

Makoto Kamada, Search for 893w

EXAMPLE

2 is in this sequence because (268*10^2 - 1)/3 = 8933 is prime.

Initial terms and primes associated:

a(1) = 0, 89;

a(2) = 2, 8933;

a(3) = 6, 89333333;

a(4) = 7, 893333333;

a(5) = 12, 89333333333333; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(268*10^# - 1)/3] &]

PROG

(PARI) isok(k) = isprime((268*10^k - 1)/3); \\ Altug Alkan, Oct 11 2017

CROSSREFS

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.

Sequence in context: A189327 A217575 A172154 * A072147 A190121 A105329

Adjacent sequences: A293528 A293529 A293530 * A293532 A293533 A293534

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Oct 11 2017

STATUS

approved

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Last modified February 3 04:55 EST 2023. Contains 360024 sequences. (Running on oeis4.)