login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A297416 Numbers k such that (17*10^k - 131)/3 is prime. 0
1, 2, 3, 6, 8, 14, 33, 56, 266, 305, 332, 435, 548, 585, 591, 890, 996, 4131, 23937, 32016, 81300 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 6 followed by the digits 23 is prime (see Example section).
a(22) > 2*10^5.
LINKS
Makoto Kamada, Search for 56w23.
EXAMPLE
2 is in this sequence because (17*10^2 - 131)/3 = 523 is prime.
Initial terms and associated primes:
a(1) = 1, 13;
a(2) = 2, 523;
a(3) = 3, 5623;
a(4) = 6, 5666623;
a(5) = 8, 566666623; etc.
MATHEMATICA
Select[Range[1, 100000], PrimeQ[(17*10^# - 131)/3] &]
PROG
(PARI) isok(k) = isprime((17*10^k - 131)/3); \\ Michel Marcus, Dec 30 2017
CROSSREFS
Sequence in context: A097097 A283474 A206370 * A304484 A095162 A075723
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Dec 29 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 22 15:57 EDT 2024. Contains 373590 sequences. (Running on oeis4.)