A282975 Numbers k such that (134*10^k + 7)/3 is prime.

0, 1, 6, 13, 18, 28, 40, 45, 50, 70, 101, 210, 248, 298, 1246, 1340, 1586, 2466, 6548, 6713, 7394, 23904, 32450, 38171, 39120, 67816, 108610, 112400, 129038

Offset

1,3

Comments

For k > 0, numbers k such that the digits 44 followed by k-1 occurrences of the digit 6 followed by the digit 9 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 446w9.

Example

1 is in this sequence because (134*10^1 + 7)/3 = 449 is prime.
Initial terms and associated primes:
a(1) = 0, 47;
a(2) = 1, 449;
a(3) = 6, 44666669;
a(4) = 13, 446666666666669;
a(5) = 18, 44666666666666666669; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(134*10^# + 7)/3] &]

Prog

(PARI) isok(k) = isprime((134*10^k + 7)/3); \\ Michel Marcus, Feb 26 2017

Crossrefs

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

Sequence in context: A153696 A032366 A287237 * A094696 A095911 A013575

Adjacent sequences: A282972 A282973 A282974 * A282976 A282977 A282978

Keyword

nonn,more,hard

Author

Robert Price, Feb 26 2017

Extensions

a(27)-a(29) from Robert Price, Feb 05 2020

Status

approved