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A293827 Numbers k such that (41*10^k - 59)/9 is prime. 0
2, 3, 11, 14, 15, 20, 23, 24, 39, 104, 374, 428, 698, 1436, 1521, 1800, 1809, 3848, 4796, 46314, 49182, 82044, 96137, 141836 (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 5 followed by the digits 49 is prime (see Example section).

a(25) > 2*10^5.

LINKS

Table of n, a(n) for n=1..24.

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

Makoto Kamada, Search for 45w49

EXAMPLE

3 is in this sequence because (41*10^3 - 59)/9 = 4549 is prime.

Initial terms and primes associated:

a(1) = 2, 449;

a(2) = 3, 4549;

a(3) = 11, 455555555549;

a(4) = 14, 455555555555549;

a(5) = 15, 4555555555555549; etc.

MATHEMATICA

Select[Range[1, 100000], PrimeQ[(41*10^# - 59)/9] &]

CROSSREFS

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

Sequence in context: A105226 A139021 A176038 * A145771 A042473 A042665

Adjacent sequences:  A293824 A293825 A293826 * A293828 A293829 A293830

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Oct 16 2017

EXTENSIONS

a(24) from Robert Price, Oct 27 2018

STATUS

approved

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Last modified March 29 15:16 EDT 2020. Contains 333107 sequences. (Running on oeis4.)