A279549 Numbers k such that (13*10^k + 47) / 3 is prime.

1, 2, 3, 9, 10, 14, 36, 44, 69, 124, 249, 297, 453, 535, 766, 1074, 1668, 1975, 1987, 2295, 5703, 6526, 13329, 34738, 37549, 39825, 93236, 99508, 136687

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 49 is prime (see Example section).

a(30) > 2*10^5.

Links

Table of n, a(n) for n=1..29.

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

Makoto Kamada, Search for 43w49.

Example

3 is in this sequence because (13*10^3 + 47) / 3 = 4349 is prime.
Initial terms and primes associated:
a(1) = 1, 59;
a(2) = 2, 449;
a(3) = 3, 4349;
a(4) = 9, 4333333349;
a(5) = 10, 43333333349; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(13*10^# + 47) / 3] &]

Prog

(PARI) is(n)=ispseudoprime((13*10^n + 47)/3) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

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

Sequence in context: A057291 A135107 A191568 * A030743 A098020 A047358

Adjacent sequences: A279546 A279547 A279548 * A279550 A279551 A279552

Keyword

nonn,more,hard

Author

Robert Price, Jan 05 2017

Extensions

a(29) from Robert Price, Oct 14 2018

Status

approved