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!)
A082182 Numbers k such that (5^k - 2^k)/3 is prime. 21

%I

%S 2,5,7,13,19,37,59,67,79,307,331,599,1301,12263,12589,18443,20149,

%T 27983

%N Numbers k such that (5^k - 2^k)/3 is prime.

%C No other terms less than 100000. - _Robert Price_, Apr 06 2012

%C All terms are primes. Some of the results were computed using the PrimeFormGW (PFGW) primality-testing program. - _Hugo Pfoertner_, Nov 14 2019

%H OEIS Wiki, <a href="http://oeis.org/wiki/Primes_of_the_form_(a%5En%2Bb%5En)/(a%2Bb)_and_(a%5En-b%5En)/(a-b)">Primes of the form (a^n+b^n)/(a+b) and (a^n-b^n)/(a-b)</a>.

%e Example: a(1)=2 because (5^2 - 2^2)/3 = (25 - 4)/3 = 7 is a prime.

%t a={};Do[p=(5^n-2^n)/3;If[PrimeQ[p],AppendTo[a,n]],{n,20^2}];Print[a]; (* _Vladimir Joseph Stephan Orlovsky_, Apr 29 2008 *)

%o (PARI) forprime(p=2,1e4,if(ispseudoprime((5^p-2^p)/3),print1(p", "))) \\ _Charles R Greathouse IV_, Jul 16, 2011

%K more,nonn

%O 1,1

%A _Hugo Pfoertner_, May 22 2003, Jun 23 2003

%E 20149 from Herman Jamke (hermanjamke(AT)fastmail.fm), May 03 2007

%E 27983 from _David Radcliffe_, May 28 2007

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 August 6 09:38 EDT 2020. Contains 336245 sequences. (Running on oeis4.)