A294485 Numbers k such that (23*10^k + 19)/3 is prime.

1, 2, 3, 4, 9, 10, 11, 17, 95, 115, 499, 1048, 1557, 3392, 4841, 5174, 11427, 12044, 14984, 16747, 38936, 44492, 110290, 149655

Offset

1,2

Comments

For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 6 followed by the digits 73 is prime (see Example section).

a(25) > 2*10^5.

Links

Table of n, a(n) for n=1..24.

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

Makoto Kamada, Search for 76w73.

Example

2 is in this sequence because (23*10^2 + 19)/3 = 773 is prime.
Initial terms and associated primes:
a(1) = 1, 83;
a(2) = 2, 773;
a(3) = 3, 7673;
a(4) = 4, 76673;
a(5) = 9, 7666666673; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(23*10^# + 19)/3] &]

Crossrefs

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

Sequence in context: A309346 A047339 A250483 * A332772 A084368 A007498

Adjacent sequences: A294482 A294483 A294484 * A294486 A294487 A294488

Keyword

nonn,more,hard

Author

Robert Price, Oct 31 2017

Extensions

a(23)-a(24) from Robert Price, Jul 27 2019

Status

approved