A282140 Numbers k such that (49*10^k + 311)/9 is prime.

1, 3, 6, 7, 9, 10, 12, 24, 39, 135, 258, 382, 660, 900, 1306, 1528, 3658, 3937, 5157, 7006, 7936, 10956, 15396, 45808, 198403

Offset

1,2

Comments

For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 4 followed by the digits 79 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 54w79.

Example

3 is in this sequence because (49*10^3 + 311)/9 = 5479 is prime.
Initial terms and primes associated:
a(1) = 1, 89;
a(2) = 3, 5479;
a(3) = 6, 5444479;
a(4) = 7, 54444479;
a(5) = 9, 5444444479; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(49*10^# + 311)/9] &]

Crossrefs

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

Sequence in context: A157319 A138933 A288938 * A071530 A005767 A085837

Adjacent sequences: A282137 A282138 A282139 * A282141 A282142 A282143

Keyword

nonn,more,hard

Author

Robert Price, Feb 06 2017

Extensions

a(25) from Robert Price, Jun 13 2019

Status

approved