A291923 Numbers k such that (482*10^k - 41)/9 is prime.

2, 3, 5, 14, 17, 23, 33, 38, 71, 242, 359, 536, 579, 629, 758, 2957, 3797, 12609, 16184, 21285, 41151

Offset

1,1

Comments

For k>1, numbers such that the digits 53 followed by k-1 occurrences of the digit 5 followed by the digit 1 is prime (see Example section).

a(22) > 2*10^5.

Links

Table of n, a(n) for n=1..21.

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

Makoto Kamada, Search for 535w1.

Example

3 is in this sequence because (482*10^3 - 41)/9 = 53551 is prime.
Initial terms and primes associated:
a(1) = 2, 5351;
a(2) = 3, 53551;
a(3) = 5, 5355551;
a(4) = 14, 5355555555555551;
a(5) = 17, 5355555555555555551; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(482*10^# - 41)/9] &]

Crossrefs

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

Sequence in context: A266192 A233082 A039575 * A283448 A177901 A143743

Adjacent sequences: A291920 A291921 A291922 * A291924 A291925 A291926

Keyword

nonn,more,hard

Author

Robert Price, Sep 05 2017

Status

approved