A295668 Numbers k such that (14*10^k + 79)/3 is prime.

0, 1, 6, 7, 8, 10, 19, 22, 42, 48, 100, 190, 298, 535, 768, 1003, 1904, 7512, 26725, 27517, 33676, 74540

Offset

1,3

Comments

For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 6 followed by the digits 93 is prime (see Example section).

a(23) > 2*10^5.

Links

Table of n, a(n) for n=1..22.

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

Makoto Kamada, Search for 46w93.

Example

1 is in this sequence because (14*10^1 + 79)/3 = 73 is prime.
Initial terms and associated primes:
a(1) = 0, 31;
a(2) = 1, 73;
a(3) = 6, 4666693;
a(4) = 7, 46666693;
a(5) = 8, 466666693; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(14*10^# + 79)/3] &] (* fixed by Shawn A. Broyles, Nov 27 2017 *)

Prog

(PARI) is(k) = ispseudoprime((14*10^k + 79)/3) \\ Iain Fox, Nov 27 2017

Crossrefs

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

Sequence in context: A209723 A261752 A248902 * A274556 A066235 A037365

Adjacent sequences: A295665 A295666 A295667 * A295669 A295670 A295671

Keyword

nonn,more,hard

Author

Robert Price, Nov 25 2017

Status

approved