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A285940 Numbers k such that (2*10^k + 67)/3 is prime. 0
0, 1, 2, 4, 7, 40, 43, 74, 98, 181, 186, 428, 532, 644, 1664, 2016, 2476, 2911, 2959, 3007, 5964, 7758, 22231, 92152 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

For k>1, numbers such that k-2 occurrences of the digit 6 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 6w89.

EXAMPLE

4 is in this sequence because (2*10^4 + 67)/3 = 6689 is prime.

Initial terms and primes associated:

a(1) = 0, 23;

a(2) = 1, 29;

a(3) = 2, 89;

a(4) = 4, 6689;

a(5) = 7, 6666689; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(2*10^# + 67)/3] &]

CROSSREFS

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

Sequence in context: A295125 A082537 A004577 * A211186 A302938 A076719

Adjacent sequences:  A285937 A285938 A285939 * A285941 A285942 A285943

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Apr 29 2017

STATUS

approved

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Last modified July 14 19:48 EDT 2020. Contains 335729 sequences. (Running on oeis4.)