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A280206 Numbers k such that (14*10^k - 53) / 3 is prime. 0
1, 2, 3, 4, 5, 11, 28, 40, 65, 95, 187, 201, 202, 211, 316, 331, 559, 746, 1307, 2139, 3571, 5843, 6545, 12717, 32804, 46389, 72326, 135301 (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 6 followed by the digits 49 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 46w49.

EXAMPLE

3 is in this sequence because (14*10^3 - 53) / 3 = 4649 is prime.

Initial terms and primes associated:

a(1) = 1, 29;

a(2) = 2, 449;

a(3) = 3, 4649;

a(4) = 4, 46649;

a(5) = 5, 466649; etc.

MATHEMATICA

Select[Range[1, 100000], PrimeQ[(14*10^# - 53) / 3] &]

PROG

(PARI) is(n)=ispseudoprime((14*10^n - 53)/3) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A064959 A217650 A032988 * A190783 A136367 A014545

Adjacent sequences:  A280203 A280204 A280205 * A280207 A280208 A280209

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Dec 28 2016

EXTENSIONS

a(28) from Robert Price, Dec 17 2018

STATUS

approved

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Last modified February 25 11:07 EST 2020. Contains 332231 sequences. (Running on oeis4.)