A279050 - OEIS

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

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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

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

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