A288482 Numbers k such that (77*10^k - 293)/9 is prime.

1, 2, 4, 7, 10, 11, 29, 35, 52, 56, 106, 217, 580, 673, 808, 1354, 1666, 3292, 3770, 8989, 16525, 24773, 39301, 125330, 158407

Offset

1,2

Comments

For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 5 followed by the digits 23 is prime (see Example section).

a(26) > 2*10^5.

Links

Table of n, a(n) for n=1..25.

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

Makoto Kamada, Search for 85w23.

Example

4 is in this sequence because (77*10^4 - 293)/9 = 85523 is prime.
Initial terms and associated primes:
a(1) = 1, 53;
a(2) = 2, 823;
a(3) = 4, 85523;
a(4) = 7, 85555523;
a(5) = 10, 85555555523; etc.

Mathematica

Select[Range[1, 100000], PrimeQ[(77*10^# - 293)/9] &]

Crossrefs

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

Sequence in context: A342782 A295837 A321972 * A177093 A164903 A285968

Adjacent sequences: A288479 A288480 A288481 * A288483 A288484 A288485

Keyword

nonn,more,hard

Author

Robert Price, Jun 09 2017

Extensions

a(24)-a(25) from Robert Price, Sep 16 2019

Status

approved