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

 

Logo

The October issue of the Notices of the Amer. Math. Soc. has an article about the OEIS.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A295969 Numbers k such that (5*10^k - 473)/9 is prime. 0
2, 3, 4, 9, 10, 16, 27, 46, 97, 103, 214, 229, 241, 285, 643, 999, 3154, 14115, 43012, 85855, 87622, 87712, 90142, 168379 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k > 1, numbers such that k-2 occurrences of the digit 5 followed by the digits 03 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 5w03

EXAMPLE

3 is in this sequence because (5*10^3 - 473)/9 = 503 is prime.

Initial terms and primes associated:

a(1) = 2, 3;

a(2) = 3, 503;

a(3) = 4, 5503;

a(4) = 9, 555555503;

a(5) = 10, 5555555503; etc.

MATHEMATICA

Select[Range[2, 100000], PrimeQ[(5*10^# - 473)/9] &]

PROG

(PARI) isok(k) = isprime((5*10^k - 473)/9); \\ Michel Marcus, Dec 01 2017

CROSSREFS

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

Sequence in context: A249943 A251620 A128944 * A174437 A127150 A256189

Adjacent sequences:  A295966 A295967 A295968 * A295970 A295971 A295972

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Nov 30 2017

EXTENSIONS

a(24) from Robert Price, Jan 21 2018

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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 25 01:17 EDT 2018. Contains 315360 sequences. (Running on oeis4.)