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A278334 Numbers n such that (856*10^n - 1) / 9 is prime. 0
2, 3, 5, 8, 9, 15, 20, 24, 41, 63, 66, 99, 281, 300, 462, 686, 726, 1196, 1574, 2543, 3023, 5322, 12161, 13677, 33797 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For n>=0, numbers such that the digits 95 followed by n occurrences of the digit 1 is prime (see Example section).

a(26) > 10^5.

LINKS

Table of n, a(n) for n=1..25.

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

Makoto Kamada, Search for 951w.

EXAMPLE

3 is in this sequence because (856*10^3 - 1) / 9 = 95111 is prime.

Initial terms and primes associated:

a(1) = 2, 9511;

a(2) = 3, 95111;

a(3) = 5, 9511111;

a(4) = 8, 9511111111;

a(5) = 9, 95111111111; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(856*10^# - 1) / 9] &]

PROG

(PARI) is(n)=ispseudoprime((856*10^n-1)/9) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A286495 A295082 A168154 * A120057 A099422 A294913

Adjacent sequences:  A278331 A278332 A278333 * A278335 A278336 A278337

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 18 2016

STATUS

approved

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Last modified February 21 18:05 EST 2020. Contains 332107 sequences. (Running on oeis4.)