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A294569 Numbers k such that (43*10^k + 101)/9 is prime. 0
1, 3, 6, 9, 12, 27, 33, 45, 63, 81, 351, 357, 540, 582, 1998, 2401, 4140, 4675, 6963, 7873, 19749, 138648, 173826, 190351 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k > 1, numbers such that the digit 4 followed by k-2 occurrences of the digit 7 followed by the digits 89 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 47w89

EXAMPLE

3 is in this sequence because (43*10^3 + 101)/9 = 4789 is prime.

Initial terms and primes associated:

a(1) = 1, 59;

a(2) = 3, 4789;

a(3) = 6, 4777789;

a(4) = 9, 4777777789;

a(5) = 12, 4777777777789; etc.

MATHEMATICA

Select[Range[1, 100000], PrimeQ[(43*10^# + 101)/9] &]

CROSSREFS

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

Sequence in context: A118519 A282762 A089757 * A277250 A083491 A086423

Adjacent sequences:  A294566 A294567 A294568 * A294570 A294571 A294572

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 02 2017

EXTENSIONS

a(22)-a(24) from Robert Price, Nov 30 2018

STATUS

approved

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Last modified December 9 17:18 EST 2019. Contains 329879 sequences. (Running on oeis4.)