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A295624 Numbers k such that (38*10^k + 403)/9 is prime. 0
2, 5, 8, 11, 15, 17, 87, 146, 201, 287, 383, 489, 527, 4077, 5102, 7769, 22715, 25077, 37425, 82161, 180296 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k > 1, numbers such that the digit 4 followed by k-2 occurrences of the digit 2 followed by the digits 67 is prime (see Example section).

a(22) > 2*10^5.

LINKS

Table of n, a(n) for n=1..21.

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

Makoto Kamada, Search for 42w67

EXAMPLE

2 is in this sequence because (38*10^82 2 161+403)/9 = 467 is prime.

Initial terms and primes associated:

a(1) = 2, 467;

a(2) = 5, 422267;

a(3) = 8, 422222267;

a(4) = 11, 422222222267;

a(5) = 15, 4222222222222267; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(38*10^# + 403)/9] &]

CROSSREFS

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

Sequence in context: A190079 A184872 A163249 * A284882 A190364 A088366

Adjacent sequences:  A295621 A295622 A295623 * A295625 A295626 A295627

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 24 2017

EXTENSIONS

a(21) from Robert Price, Oct 03 2018

STATUS

approved

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Last modified August 17 11:49 EDT 2022. Contains 356189 sequences. (Running on oeis4.)