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A281167 Numbers k such that (23*10^k - 143)/3 is prime. 0
1, 2, 6, 7, 14, 22, 31, 33, 42, 51, 799, 934, 1996, 3372, 3570, 3883, 4417, 4747, 4965, 5055, 5647, 7183, 19702, 42124, 180862, 187164 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 6 followed by the digits 19 is prime (see Example section).

a(27) > 2*10^5.

LINKS

Table of n, a(n) for n=1..26.

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

Makoto Kamada, Search for 76w19.

EXAMPLE

2 is in this sequence because (23*10^2 - 143) / 3 = 719 is prime.

Initial terms and primes associated:

a(1) = 1, 29;

a(2) = 2, 719;

a(3) = 6, 7666619;

a(4) = 7, 76666619;

a(5) = 14, 766666666666619; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(23*10^# - 143) / 3] &]

CROSSREFS

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

Sequence in context: A199974 A176279 A265739 * A210660 A226965 A128918

Adjacent sequences:  A281164 A281165 A281166 * A281168 A281169 A281170

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Jan 16 2017

EXTENSIONS

a(25)-a(26) from Robert Price, Dec 04 2019

STATUS

approved

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Last modified May 31 01:29 EDT 2020. Contains 334747 sequences. (Running on oeis4.)