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A294229 Numbers k such that (52*10^k + 119)/9 is prime. 0
0, 1, 3, 4, 9, 12, 13, 15, 30, 37, 58, 67, 142, 355, 442, 660, 1078, 3337, 5923, 10204, 21645, 50149 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 7 followed by the digits 91 is prime (see Example section).

a(23) > 2*10^5.

LINKS

Table of n, a(n) for n=1..22.

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

Makoto Kamada, Search for 57w91.

EXAMPLE

3 is in this sequence because (52*10^3 + 119)/9 = 5791 is prime.

Initial terms and primes associated:

a(1) = 0, 19;

a(2) = 1, 71;

a(3) = 3, 5791;

a(4) = 4, 57791;

a(5) = 9, 5777777791; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(52*10^# + 119)/9] &]

CROSSREFS

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

Sequence in context: A327060 A270817 A182828 * A035256 A287400 A309758

Adjacent sequences:  A294226 A294227 A294228 * A294230 A294231 A294232

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Oct 25 2017

STATUS

approved

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Last modified October 22 13:49 EDT 2021. Contains 348170 sequences. (Running on oeis4.)