A294228 Numbers k such that (17*10^k + 43)/3 is prime.

1, 4, 5, 6, 7, 12, 23, 34, 160, 719, 725, 2568, 3095, 3520, 3582, 3791, 4198, 5236, 15445, 26431, 33120, 36028

Offset

1,2

Comments

For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 6 followed by the digits 81 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 56w81.

Example

4 is in this sequence because (17*10^4 + 43)/3 = 56681 is prime.
Initial terms and primes associated:
a(1) = 1, 71;
a(2) = 4, 56681;
a(3) = 5, 566681;
a(4) = 6, 5666681;
a(5) = 7, 56666681; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(17*10^# + 43)/3] &]

Crossrefs

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

Sequence in context: A047566 A283775 A037355 * A342575 A046300 A053738

Adjacent sequences: A294225 A294226 A294227 * A294229 A294230 A294231

Keyword

nonn,more,hard

Author

Robert Price, Oct 25 2017

Status

approved