login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A293274 Numbers k such that (23*10^k - 47)/3 is prime. 0
1, 2, 4, 5, 11, 28, 34, 35, 36, 49, 65, 90, 126, 1878, 2089, 3266, 3818, 6485, 7710, 8539, 20603, 34764, 51283, 176964 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k > 1, numbers such that the digit 7 followed by k-2 occurrences of the digit 6 followed by the digits 51 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 76w51.

EXAMPLE

4 is in this sequence because (23*10^4 - 47)/3 = 76651 is prime.

Initial terms and primes associated:

a(1) = 1, 61;

a(2) = 2, 751;

a(3) = 4, 76651;

a(4) = 5, 766651;

a(5) = 11, 766666666651; etc.

MATHEMATICA

Select[Range[1, 100000], PrimeQ[(23*10^# - 47)/3] &]

CROSSREFS

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

Sequence in context: A095022 A279050 A317828 * A101961 A285055 A268530

Adjacent sequences:  A293271 A293272 A293273 * A293275 A293276 A293277

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Oct 04 2017

EXTENSIONS

a(24) from Robert Price, Sep 22 2019

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 October 21 06:25 EDT 2019. Contains 328292 sequences. (Running on oeis4.)