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A290962 Numbers k such that (13*10^k - 43)/3 is prime. 1
1, 2, 4, 5, 8, 12, 55, 125, 136, 221, 224, 668, 1254, 2639, 4745, 5888, 8526, 9139, 13771, 17936, 27713, 38668, 44680, 73891, 135184 (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 3 followed by the digits 19 is prime (see Example section).

a(26) > 2*10^5.

LINKS

Table of n, a(n) for n=1..25.

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

Makoto Kamada, Search for 43w19.

EXAMPLE

2 is in this sequence because (13*10^2 - 43)/3 = 419 is prime.

Initial terms and primes associated:

a(1) = 1, 29;

a(2) = 2, 419;

a(3) = 4, 43319;

a(4) = 5; 433319;

a(5) = 8, 433333319; etc.

MATHEMATICA

Select[Range[1, 100000], PrimeQ[(13*10^# - 43)/3] &]

PROG

(PARI) isok(n) = ispseudoprime((13*10^n - 43)/3) \\ Altug Alkan, Aug 15 2017

CROSSREFS

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

Sequence in context: A238395 A116901 A244487 * A102829 A031988 A023745

Adjacent sequences:  A290959 A290960 A290961 * A290963 A290964 A290965

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Aug 15 2017

EXTENSIONS

a(25) from Robert Price, Nov 28 2018

STATUS

approved

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Last modified October 16 01:33 EDT 2019. Contains 328038 sequences. (Running on oeis4.)