A294633 Numbers k such that (76*10^k + 77)/9 is prime.

0, 2, 5, 9, 24, 50, 63, 98, 117, 164, 932, 1086, 3465, 5706, 6311, 6440, 8985, 10397, 14157, 23528, 100611, 144648, 164984

Offset

1,2

Comments

For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 4 followed by the digits 53 is prime (see Example section).

a(24) > 2*10^5.

Links

Table of n, a(n) for n=1..23.

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

Makoto Kamada, Search for 84w53.

Example

2 is in this sequence because (76*10^2 + 77)/9 = 853 is prime.
Initial terms and associated primes:
a(1) = 0, 17;
a(2) = 2, 853;
a(3) = 5, 844453;
a(4) = 9, 8444444453;
a(5) = 24, 8444444444444444444444453; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(76*10^# + 77)/9] &]

Crossrefs

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

Sequence in context: A109621 A075200 A075198 * A320798 A364267 A006405

Adjacent sequences: A294630 A294631 A294632 * A294634 A294635 A294636

Keyword

nonn,more,hard

Author

Robert Price, Nov 05 2017

Extensions

a(21)-a(23) from Robert Price, Sep 30 2019

Status

approved