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!)
A280557 Numbers k such that (11*10^k - 113) / 3 is prime. 0
4, 6, 13, 15, 23, 25, 31, 71, 133, 333, 341, 905, 1027, 3667, 7241, 8217, 8493, 9816, 11842, 15454, 15891, 19117, 30424, 35196, 42808, 78408, 95641, 177466 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 6 followed by the digits 29 is prime (see Example section).
a(28) > 2*10^5.
LINKS
Makoto Kamada, Search for 36w29.
EXAMPLE
6 is in this sequence because (11*10^6 - 113) / 3 = 3666629 is prime.
Initial terms and associated primes:
a(1) = 4, 36629;
a(2) = 6, 3666629;
a(3) = 13, 36666666666629;
a(4) = 15, 3666666666666629;
a(5) = 23, 366666666666666666666629; etc.
MATHEMATICA
Select[Range[2, 100000], PrimeQ[(11*10^# - 113) / 3] &]
PROG
(PARI) is(n)=ispseudoprime((11*10^n - 113)/3) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
Sequence in context: A074165 A137821 A010061 * A266665 A249715 A249440
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jan 05 2017
EXTENSIONS
a(28) from Robert Price, Oct 10 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 20 07:26 EDT 2024. Contains 373512 sequences. (Running on oeis4.)