%I #25 Nov 09 2024 17:03:59

%S 1,2,3,5,8,14,23,63,107,132,428,530,1137,1973,2000,7064,20747,79574,

%T 113570,293912,1993191

%N Numbers n such that n*4^n-1 is prime.

%C 2, 3, 5, 23, 107, 1973, 20747 is the subsequence of prime terms.

%D H. Dubner, Generalized Cullen Numbers, J. Rec. Math, 21 (No. 3, 1989).

%H Steven Harvey, <a href="http://harvey563.tripod.com/GeneralizedWoodallPrimes.txt">Generalized Woodall Search</a>

%e 2 is in the sequence because 2*4^2-1=31 is prime.

%e 3 is in the sequence because 3*4^3-1=191 is prime.

%t Do[If[PrimeQ[n*4^n-1], Print[n]], {n, 4000}]

%t Select[Range[2000],PrimeQ[# 4^#-1]&] (* _Harvey P. Dale_, Nov 09 2024 *)

%o (PARI) is(n)=ispseudoprime(n*4^n-1) \\ _Charles R Greathouse IV_, May 22 2017

%Y Cf. A007646, A002234, A005849.

%K nonn,more,changed

%O 1,2

%A _Farideh Firoozbakht_, Jul 27 2003

%E One more term from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 23 2004

%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008

%E Prepended first terms 1 and 2 - _Pierre CAMI_, Jul 21 2014

%E a(20)-a(21) from Harvey link by _Ray Chandler_, Apr 10 2016