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A295626 Numbers k such that (424*10^k - 1)/9 is prime. 0
0, 3, 11, 33, 53, 78, 111, 144, 155, 191, 258, 687, 927, 1829, 5406, 11027, 14526, 19758, 20658, 37865, 61770, 87930 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k > 1, numbers such that the digits 47 followed by k occurrences of the digit 1 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 471w.

EXAMPLE

3 is in this sequence because (424*10^3 - 1)/9 = 47111 is prime.

Initial terms and primes associated:

a(1) = 0, 47;

a(2) = 3, 47111;

a(3) = 11, 4711111111111;

a(4) = 33, 47111111111111111111111111111111111; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(424*10^# - 11)/9] &]

CROSSREFS

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

Sequence in context: A125671 A034561 A131747 * A079996 A288038 A186308

Adjacent sequences:  A295623 A295624 A295625 * A295627 A295628 A295629

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 24 2017

STATUS

approved

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Last modified May 26 02:45 EDT 2022. Contains 354074 sequences. (Running on oeis4.)