A086661 Numbers k such that k*4^k-1 is prime.
1, 2, 3, 5, 8, 14, 23, 63, 107, 132, 428, 530, 1137, 1973, 2000, 7064, 20747, 79574, 113570, 293912, 1993191
Offset: 1
Examples
2 is in the sequence because 2*4^2-1=31 is prime. 3 is in the sequence because 3*4^3-1=191 is prime.
References
- H. Dubner, Generalized Cullen Numbers, J. Rec. Math, 21 (No. 3, 1989).
Links
- Steven Harvey, Generalized Woodall Search
Programs
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Mathematica
Do[If[PrimeQ[n*4^n-1], Print[n]], {n, 4000}] Select[Range[2000],PrimeQ[# 4^#-1]&] (* Harvey P. Dale, Nov 09 2024 *) -
PARI
is(n)=ispseudoprime(n*4^n-1) \\ Charles R Greathouse IV, May 22 2017
Extensions
One more term from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 23 2004
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008
Prepended first terms 1 and 2 - Pierre CAMI, Jul 21 2014
a(20)-a(21) from Harvey link by Ray Chandler, Apr 10 2016
Comments