A293913 Numbers k such that (436*10^k - 13)/9 is prime.

0, 5, 8, 9, 12, 39, 68, 78, 98, 200, 218, 359, 1064, 1127, 1355, 2868, 4940, 7236, 12050, 24708, 47214, 52683

Offset

1,2

Comments

For k > 1, numbers k such that the digits 48 followed by k-1 occurrences of the digit 4 followed by the digit 3 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 484w3.

Example

5 is in this sequence because (436*10^5 - 13)/9 = 4844443 is prime.
Initial terms and associated primes:
a(1) = 0, 47;
a(2) = 5, 4844443;
a(3) = 8, 4844444443;
a(4) = 9, 48444444443;
a(5) = 12, 48444444444443; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(436*10^# - 13)/9] &]

Crossrefs

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

Sequence in context: A314574 A314575 A286454 * A213881 A179832 A334919

Adjacent sequences: A293910 A293911 A293912 * A293914 A293915 A293916

Keyword

nonn,more,hard

Author

Robert Price, Oct 19 2017

Status

approved