A293825 Numbers k such that (29*10^k + 673)/9 is prime.

1, 2, 4, 7, 14, 19, 20, 22, 29, 40, 64, 169, 173, 1513, 2357, 3193, 4198, 11864, 18182, 19576, 31175, 38030, 57967, 122996

Offset

1,2

Comments

For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 2 followed by the digits 97 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 32w97.

Example

2 is in this sequence because (29*10^2 + 673)/9 = 397 is prime.
Initial terms and associated primes:
a(1) = 1, 107;
a(2) = 2, 397;
a(3) = 4, 32297;
a(4) = 7, 32222297;
a(5) = 14, 322222222222297; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(29*10^# + 673)/9] &]

Crossrefs

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

Sequence in context: A248220 A018476 A265309 * A289050 A133638 A367266

Adjacent sequences: A293822 A293823 A293824 * A293826 A293827 A293828

Keyword

nonn,more,hard

Author

Robert Price, Oct 16 2017

Extensions

a(24) from Robert Price, Dec 07 2018

Status

approved