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A282667 Numbers k such that (7*10^k + 107)/3 is prime. 0
1, 2, 4, 8, 12, 15, 21, 31, 48, 151, 723, 879, 1811, 3444, 5104, 5512, 5695, 6723, 9082, 14944, 15184, 18512, 35141, 81985, 123563, 155203, 165134, 165239 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers such that the digit 2 followed by k-2 occurrences of the digit 3 followed by the digits 69 is prime (see Example section).

a(29) > 2*10^5.

LINKS

Table of n, a(n) for n=1..28.

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

Makoto Kamada, Search for 23w69.

EXAMPLE

4 is in this sequence because (7*10^4 + 107)/3 = 23369 is prime.

Initial terms and primes associated:

a(1) = 1, 59;

a(2) = 2, 269;

a(3) = 4, 23369;

a(4) = 8, 233333369;

a(5) = 12, 2333333333369; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(7*10^# + 107)/3] &]

CROSSREFS

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

Sequence in context: A064711 A050865 A288514 * A124395 A334167 A024908

Adjacent sequences:  A282664 A282665 A282666 * A282668 A282669 A282670

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Feb 20 2017

EXTENSIONS

a(25)-a(28) from Robert Price, Feb 21 2018

STATUS

approved

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Last modified December 3 02:56 EST 2020. Contains 338899 sequences. (Running on oeis4.)