A293536 Numbers k such that (19*10^k + 737)/9 is prime.

1, 2, 4, 5, 8, 16, 17, 77, 124, 284, 287, 988, 3277, 4123, 5290, 12317, 18280, 18302, 20266, 20665, 41420, 56224, 100997, 174754

Offset

1,2

Comments

For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 1 followed by the digits 93 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 21w93.

Example

2 is in this sequence because (19*10^2 + 737)/9 = 293 is prime.
Initial terms and associated primes:
a(1) = 1, 103;
a(2) = 2, 293;
a(3) = 4, 21193;
a(4) = 5, 211193;
a(5) = 8, 211111193; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(19*10^# + 737)/9] &]

Crossrefs

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

Sequence in context: A229083 A194415 A364779 * A274796 A160967 A326173

Adjacent sequences: A293533 A293534 A293535 * A293537 A293538 A293539

Keyword

nonn,more,hard

Author

Robert Price, Oct 11 2017

Extensions

a(23)-a(24) from Robert Price, Jul 13 2018

Status

approved