A280924 Numbers k such that 8*10^k + 39 is prime.

0, 2, 3, 4, 14, 27, 35, 42, 53, 60, 89, 117, 126, 137, 162, 207, 281, 472, 2752, 3381, 6462, 12183, 14910, 29205, 40883, 50675, 78717, 83880, 99113

Offset

1,2

Comments

For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 0 followed by the digits 39 is prime (see Example section).

a(30) > 2*10^5.

Links

Table of n, a(n) for n=1..29.

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

Makoto Kamada, Search for 80w39.

Example

3 is in this sequence because 8*10^3 + 39 = 8039 is prime.
Initial terms and associated primes:
a(1) = 0, 47;
a(2) = 2, 839;
a(3) = 3, 8039;
a(4) = 4, 80039;
a(5) = 14, 800000000000039; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[8*10^# + 39] &]

Crossrefs

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

Sequence in context: A317737 A188533 A163128 * A295756 A140047 A297840

Adjacent sequences: A280921 A280922 A280923 * A280925 A280926 A280927

Keyword

nonn,more,hard

Author

Robert Price, Jan 10 2017

Status

approved