login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A286176 Numbers k such that (209*10^k - 17)/3 is prime. 0
1, 2, 3, 7, 13, 14, 37, 38, 54, 60, 69, 668, 693, 825, 1275, 1566, 3129, 5745, 6439, 21991, 24992, 61947, 96722 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k>0, numbers such that the digits 69 followed by k-1 occurrences of the digit 6 followed by the digit 1 is prime (see Example section).

a(24) > 10^5.

LINKS

Table of n, a(n) for n=1..23.

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

Makoto Kamada, Search for 696w1.

EXAMPLE

3 is in this sequence because (209*10^3 - 17)/3 = 69661 is prime.

Initial terms and primes associated:

a(1) = 1, 691;

a(2) = 2, 6961;

a(3) = 3, 69661;

a(4) = 7, 696666661;

a(5) = 13, 696666666666661; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(209*10^# - 17)/3] &]

CROSSREFS

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

Sequence in context: A084955 A273056 A026472 * A318401 A322703 A225098

Adjacent sequences:  A286173 A286174 A286175 * A286177 A286178 A286179

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, May 03 2017

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 3 20:29 EDT 2020. Contains 333199 sequences. (Running on oeis4.)