A281275 Numbers k such that (19*10^k + 467)/9 is prime.

1, 2, 4, 7, 8, 14, 19, 34, 40, 55, 178, 251, 314, 410, 982, 1198, 1604, 2486, 2642, 3928, 19231, 24874, 28850, 143963

Offset

1,2

Comments

For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 1 followed by the digits 63 is prime (see Example section).

a(25) > 2*10^5.

Links

Table of n, a(n) for n=1..24.

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

Makoto Kamada, Search for 21w63.

Example

2 is in this sequence because (19*10^2 + 467)/9 = 263 is prime.
Initial terms and associated primes:
a(1) = 1, 73;
a(2) = 2, 263;
a(3) = 4, 21163;
a(4) = 7, 21111163;
a(5) = 8, 211111163; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(19*10^# + 467)/9] &]

Crossrefs

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

Sequence in context: A018289 A128395 A018740 * A015893 A018430 A018265

Adjacent sequences: A281272 A281273 A281274 * A281276 A281277 A281278

Keyword

nonn,more,hard

Author

Robert Price, Jan 18 2017

Extensions

a(24) from Robert Price, Feb 14 2018

Status

approved