A279050 Numbers k such that (14*10^k - 143)/3 is prime.

2, 4, 5, 11, 23, 27, 28, 60, 114, 154, 160, 194, 412, 417, 769, 1189, 3845, 5381, 10905, 11192, 11630, 19737, 56080, 155740, 259431, 282673

Offset

1,1

Comments

For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 6 followed by the digits 19 is prime (see Example section).

a(27) > 3*10^5.

Links

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

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

Makoto Kamada, Search for 46w19.

Example

4 is in this sequence because (14*10^4 - 143) / 3 = 46619 is prime.
Initial terms and associated primes:
a(1) = 2, 419;
a(2) = 4, 46619;
a(3) = 5, 466619;
a(4) = 11, 466666666619;
a(5) = 23, 466666666666666666666619; etc.

Mathematica

Select[Range[2, 100000], PrimeQ[(14*10^# - 143) / 3] &]

Crossrefs

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

Sequence in context: A113058 A066145 A095022 * A317828 A293274 A101961

Adjacent sequences: A279047 A279048 A279049 * A279051 A279052 A279053

Keyword

nonn,more,hard

Author

Robert Price, Jan 05 2017

Extensions

a(24) from Robert Price, Nov 07 2018

a(25)-a(26) from Robert Price, Jul 12 2023

Status

approved