A295667 Numbers k such that (22*10^k + 383)/9 is prime.

1, 10, 16, 19, 28, 43, 76, 91, 125, 203, 283, 911, 2416, 2633, 4735, 4876, 4900, 7825, 26969, 51154, 169019

Offset

1,2

Comments

For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 4 followed by the digits 87 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 24w87.

Example

1 is in this sequence because (22*10^1 + 383)/9 = 67 is prime.
Initial terms and associated primes:
a(1) = 1, 67;
a(2) = 10, 24444444487;
a(3) = 16, 24444444444444487;
a(4) = 19, 24444444444444444487;
a(5) = 28, 24444444444444444444444444487; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(22*10^# + 383)/9] &]

Crossrefs

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

Sequence in context: A106695 A053747 A228491 * A241763 A233579 A291639

Adjacent sequences: A295664 A295665 A295666 * A295668 A295669 A295670

Keyword

nonn,more,hard

Author

Robert Price, Nov 25 2017

Extensions

a(21) from Robert Price, May 27 2018

Status

approved