A280018 Numbers k such that 34*10^k - 3 is prime.

0, 1, 3, 5, 7, 11, 14, 20, 25, 35, 36, 117, 164, 372, 453, 649, 1743, 1748, 1897, 2323, 6351, 16599, 25017, 25736, 27866

Offset

1,3

Comments

For k > 0, numbers k such that the digits 33 followed by k-1 occurrences of the digit 9 followed by the digit 7 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 339w7.

Example

3 is in this sequence because 34*10^3 - 3 = 33997 is prime.
Initial terms and associated primes:
a(1) = 0, 31;
a(2) = 1, 337;
a(3) = 3, 33997;
a(4) = 5, 3399997;
a(5) = 7, 339999997; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[34*10^# - 3] &]

Crossrefs

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

Sequence in context: A087325 A072151 A332028 * A029626 A111622 A356065

Adjacent sequences: A280015 A280016 A280017 * A280019 A280020 A280021

Keyword

nonn,more,hard

Author

Robert Price, Feb 21 2017

Status

approved