# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a086661 Showing 1-1 of 1 %I A086661 #25 Nov 09 2024 17:03:59 %S A086661 1,2,3,5,8,14,23,63,107,132,428,530,1137,1973,2000,7064,20747,79574, %T A086661 113570,293912,1993191 %N A086661 Numbers n such that n*4^n-1 is prime. %C A086661 2, 3, 5, 23, 107, 1973, 20747 is the subsequence of prime terms. %D A086661 H. Dubner, Generalized Cullen Numbers, J. Rec. Math, 21 (No. 3, 1989). %H A086661 Steven Harvey, Generalized Woodall Search %e A086661 2 is in the sequence because 2*4^2-1=31 is prime. %e A086661 3 is in the sequence because 3*4^3-1=191 is prime. %t A086661 Do[If[PrimeQ[n*4^n-1], Print[n]], {n, 4000}] %t A086661 Select[Range[2000],PrimeQ[# 4^#-1]&] (* _Harvey P. Dale_, Nov 09 2024 *) %o A086661 (PARI) is(n)=ispseudoprime(n*4^n-1) \\ _Charles R Greathouse IV_, May 22 2017 %Y A086661 Cf. A007646, A002234, A005849. %K A086661 nonn,more,changed %O A086661 1,2 %A A086661 _Farideh Firoozbakht_, Jul 27 2003 %E A086661 One more term from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 23 2004 %E A086661 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008 %E A086661 Prepended first terms 1 and 2 - _Pierre CAMI_, Jul 21 2014 %E A086661 a(20)-a(21) from Harvey link by _Ray Chandler_, Apr 10 2016 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE