A293002 Numbers k such that (62*10^k - 791)/9 is prime.

2, 7, 10, 34, 53, 59, 62, 241, 298, 485, 731, 899, 1231, 4702, 7010, 8573, 9205, 9724, 17045, 24950, 136384

Offset

1,1

Comments

For k>1, numbers such that the digit 6 followed by k-2 occurrences of the digit 8 followed by the digits 01 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 68w01.

Example

2 is in this sequence because (62*10^2 - 791)/9 = 601 is prime.
Initial terms and primes associated:
a(1) = 2, 601;
a(2) = 7, 68888801;
a(3) = 10, 68888888801;
a(4) = 34, 68888888888888888888888888888888801;
a(5) = 53, 688888888888888888888888888888888888888888888888888801; etc.

Mathematica

Select[Range[1, 100000], PrimeQ[(62*10^# - 791)/9] &]

Crossrefs

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

Sequence in context: A215407 A084184 A015963 * A056656 A351240 A151346

Adjacent sequences: A292999 A293000 A293001 * A293003 A293004 A293005

Keyword

nonn,more,hard

Author

Robert Price, Sep 27 2017

Extensions

a(21) from Robert Price, Jun 02 2019

Status

approved