A294380 Numbers k such that 8*10^k - 67 is prime.

1, 2, 3, 14, 95, 123, 135, 144, 155, 221, 239, 324, 462, 830, 3462, 4124, 9195, 9767, 24956, 26744, 98111, 185529

Offset

1,2

Comments

For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 9 followed by the digits 33 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 79w33.

Example

2 is in this sequence because 8*10^2 - 67 = 733 is prime.
Initial terms and primes associated:
a(1) = 1, 13;
a(2) = 2, 733;
a(3) = 3, 7933;
a(4) = 14, 799999999999933; etc.

Mathematica

Select[Range[1, 100000], PrimeQ[8*10^# - 67] &]

Crossrefs

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

Sequence in context: A203761 A154750 A041167 * A343261 A308128 A006279

Adjacent sequences: A294377 A294378 A294379 * A294381 A294382 A294383

Keyword

nonn,more,hard

Author

Robert Price, Oct 29 2017

Extensions

a(22) from Robert Price, Aug 05 2019

Status

approved