A291607 Numbers k such that (46*10^k + 521)/9 is prime.

1, 2, 4, 5, 8, 29, 43, 62, 85, 107, 172, 557, 1043, 2395, 4498, 5818, 7772, 9125, 12616, 17252, 23000, 64904, 71077, 113162

Offset

1,2

Comments

For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 1 followed by the digits 69 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 51w69.

Example

4 is in this sequence because (46*10^4 + 521)/9 = 51169 is prime.
Initial terms and associated primes:
a(1) = 1, 109;
a(2) = 2, 569;
a(3) = 4, 51169;
a(4) = 5, 511169;
a(5) = 8, 511111169; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(46*10^# + 521)/9] &]

Crossrefs

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

Sequence in context: A277289 A218347 A171411 * A092752 A152603 A159260

Adjacent sequences: A291604 A291605 A291606 * A291608 A291609 A291610

Keyword

nonn,more,hard

Author

Robert Price, Aug 27 2017

Extensions

a(24) from Robert Price, Feb 23 2019

Status

approved