A294128 Numbers k such that (44*10^k - 233)/9 is prime.

2, 7, 28, 49, 64, 185, 239, 364, 848, 1613, 1772, 1784, 2296, 3020, 5255, 6575, 8848, 12377, 18442, 32944, 57721, 64192, 108544, 127169, 132233

Offset

1,1

Comments

For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 8 followed by the digits 63 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 48w63.

Example

2 is in this sequence because (44*10^2 - 233)/9 = 463 is prime.
Initial terms and associated primes:
a(1) = 2, 463;
a(2) = 7, 48888863;
a(3) = 28, 48888888888888888888888888863;
a(4) = 49, 48888888888888888888888888888888888888888888888863;  etc.

Mathematica

Select[Range[2, 100000], PrimeQ[(44*10^# - 233)/9] &]

Crossrefs

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

Sequence in context: A255487 A077622 A137108 * A099815 A123363 A102961

Adjacent sequences: A294125 A294126 A294127 * A294129 A294130 A294131

Keyword

nonn,more,hard

Author

Robert Price, Oct 23 2017

Extensions

a(23)-a(25) from Robert Price, Jan 27 2019

Status

approved