login

Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.

Numbers k such that |2^(2*k-27)-27| is prime.
0

%I #26 Sep 14 2024 02:17:07

%S 15,16,17,23,25,305,1277,2675,3179,8987,9013,27493,42703

%N Numbers k such that |2^(2*k-27)-27| is prime.

%C a(14) > 10^5. - _Michael S. Branicky_, Sep 13 2024

%e 2^(2*17-27)-27=101, 2^(2*23-27)-27=524261, 2^(2*25-27)-27=8388581, ...

%t q=27; For[i=q, i<=q, a={}; Do[x=2^(2*n-i)-i; If[PrimeQ[x], AppendTo[a,n]], {n,20^2}]; Print["2^(2*n-",i,")-",i," ",a]; i=i+2]

%t Select[Range[1000],PrimeQ[Abs[2^(2#-27)-27]]&] (* _Harvey P. Dale_, Nov 12 2015 *)

%o (PARI) is(n)=ispseudoprime(abs(2^(2*n-27)-27)) \\ _Charles R Greathouse IV_, Jun 13 2017

%K more,nonn

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, May 13 2008

%E a(7)-a(11) from _Iain Fox_, Jan 13 2018

%E a(12) from _Iain Fox_, Jan 16 2018

%E a(13) from _Iain Fox_, Jan 18 2018