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A272059 Numbers k such that (17*10^k + 13)/3 is prime. 0
1, 2, 4, 7, 10, 13, 15, 20, 22, 33, 34, 108, 117, 130, 193, 273, 280, 654, 775, 1144, 4014, 4015, 7701, 10356, 11478, 12427, 15075, 44107, 102597, 118635 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>1, numbers n such that the digit 5 followed by k-2 occurrences of the digit 6 followed by the digits 71 is prime (see Example section).

a(31) > 2*10^5.

LINKS

Table of n, a(n) for n=1..30.

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

Makoto Kamada, Search for 56w71.

EXAMPLE

4 is in this sequence because (17*10^4 + 13)/3 = 56671 is prime.

Initial terms and primes associated:

a(1) = 1, 61;

a(2) = 2, 571:

a(3) = 4, 56671;

a(4) = 7, 56666671;

a(5) = 10, 56666666671, etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(17*10^# + 13)/3] &]

PROG

(PARI) is(n)=ispseudoprime((17*10^n + 13)/3) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

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

Sequence in context: A122019 A190279 A186325 * A033627 A066512 A304116

Adjacent sequences:  A272056 A272057 A272058 * A272060 A272061 A272062

KEYWORD

nonn,more

AUTHOR

Robert Price, May 19 2016

EXTENSIONS

a(29)-a(30) from Robert Price, Jan 22 2019

STATUS

approved

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Last modified May 21 23:31 EDT 2019. Contains 323469 sequences. (Running on oeis4.)