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A279467 Numbers k such that (14*10^k - 71) / 3 is prime. 0
1, 2, 3, 4, 6, 10, 14, 22, 25, 31, 43, 63, 123, 430, 508, 1457, 1701, 3371, 3429, 3548, 4582, 7463, 8852, 10594, 30621, 143662 (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 43 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 46w43.

EXAMPLE

4 is in this sequence because (14*10^4 - 71) / 3 = 46643 is prime.

Initial terms and primes associated:

a(1) = 1, 23;

a(2) = 2, 443;

a(3) = 3, 4643;

a(4) = 4, 46643;

a(5) = 6, 4666643; etc.

MATHEMATICA

Select[Range[1, 100000], PrimeQ[(14*10^# - 71) / 3] &]

PROG

(MAGMA) [n: n in [1..500] |IsPrime((14*10^n - 71) div 3)]; // Vincenzo Librandi Dec 14 2016

(PARI) is(n)=ispseudoprime((14*10^n - 71)/3) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A256248 A089223 A240057 * A094861 A173473 A288807

Adjacent sequences:  A279464 A279465 A279466 * A279468 A279469 A279470

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Dec 12 2016

EXTENSIONS

a(26) from Robert Price, Dec 28 2018

STATUS

approved

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Last modified January 27 03:09 EST 2022. Contains 350601 sequences. (Running on oeis4.)