A294990 Numbers k such that (22*10^k + 257)/9 is prime.

1, 3, 4, 6, 22, 31, 201, 265, 340, 388, 396, 561, 1224, 2841, 3234, 3538, 8473, 12061, 29347, 62926, 146029

Offset

1,2

Comments

For k > 1, numbers such that the digit 2 followed by k-2 occurrences of the digit 4 followed by the digits 73 is prime (see Example section).

a(22) > 2*10^5.

Links

Table of n, a(n) for n=1..21.

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

Makoto Kamada, Search for 24w73

Example

3 is in this sequence because (22*10^3 + 257)/9 = 2473 is prime.
Initial terms and primes associated:
a(1) = 1, 53;
a(2) = 3, 2473;
a(3) = 4, 24473;
a(4) = 6, 2444473;
a(5) = 22, 24444444444444444444473; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(22*10^# + 257)/9] &]

Crossrefs

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

Sequence in context: A304679 A265735 A038520 * A081888 A306493 A019209

Adjacent sequences: A294987 A294988 A294989 * A294991 A294992 A294993

Keyword

nonn,more,hard

Author

Robert Price, Nov 12 2017

Extensions

a(21) from Robert Price, Jun 08 2018

Status

approved