A284779 Numbers k such that (13*10^k + 161)/3 is prime.

1, 2, 17, 34, 52, 54, 495, 505, 572, 750, 959, 1574, 2557, 3734, 4069, 11201, 13411, 16569, 17032, 17720, 19906, 23781, 36076, 56624, 84179, 117249, 159147

Offset

1,2

Comments

For k>1, numbers such that the digit 4 followed by k-2 occurrences of the digit 3 followed by the digits 87 is prime (see Example section).

a(28) > 2*10^5.

Links

Table of n, a(n) for n=1..27.

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

Makoto Kamada, Search for 43w87.

Example

4 is in this sequence because (13*10^2 + 161)/3 = 487 is prime.
Initial terms and primes associated:
a(1) = 1, 97;
a(2) = 2, 487;
a(3) = 17, 433333333333333387;
a(4) = 34, 43333333333333333333333333333333387;
a(5) = 52, 43333333333333333333333333333333333333333333333333387; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(13*10^# + 161)/3] &]

Prog

(PARI) isok(n) = isprime((13*10^n + 161)/3); \\ Indranil Ghosh, Apr 02 2017

Crossrefs

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

Sequence in context: A307690 A100294 A192453 * A018529 A342485 A342487

Adjacent sequences: A284776 A284777 A284778 * A284780 A284781 A284782

Keyword

nonn,more,hard

Author

Robert Price, Apr 02 2017

Extensions

a(26)-a(27) from Robert Price, Nov 29 2018

Status

approved