A293592 Numbers k such that 3*10^k - 59 is prime.

2, 5, 7, 55, 70, 188, 248, 273, 385, 416, 479, 530, 574, 892, 1833, 4057, 4299, 6188, 14699, 21121, 88293, 89608, 95776, 162620, 196881

Offset

1,1

Comments

For k>1, numbers such that the digit 2 followed by k-2 occurrences of the digit 9 followed by the digits 41 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 29w41

Example

2 is in this sequence because (3*10^2 - 59)/3 = 241 is prime.
Initial terms and primes associated:
a(1) = 2, 241;
a(2) = 5, 299941;
a(3) = 7, 29999941;
a(4) = 55, 29999999999999999999999999999999999999999999999999999941; etc.

Mathematica

Select[Range[2, 100000], PrimeQ[(3*10^# - 59)/3] &]

Crossrefs

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

Sequence in context: A182785 A358381 A041125 * A042257 A343833 A103056

Adjacent sequences: A293589 A293590 A293591 * A293593 A293594 A293595

Keyword

nonn,more,hard

Author

Robert Price, Oct 12 2017

Extensions

a(24)-a(25) from Robert Price, Sep 08 2018

Status

approved