OFFSET
1,2
COMMENTS
2, 3, 5, 23, 107, 1973, 20747 is the subsequence of prime terms.
REFERENCES
H. Dubner, Generalized Cullen Numbers, J. Rec. Math, 21 (No. 3, 1989).
LINKS
Steven Harvey, Generalized Woodall Search
EXAMPLE
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.
MATHEMATICA
Do[If[PrimeQ[n*4^n-1], Print[n]], {n, 4000}]
Select[Range[2000], PrimeQ[# 4^#-1]&] (* Harvey P. Dale, Nov 09 2024 *)
PROG
(PARI) is(n)=ispseudoprime(n*4^n-1) \\ Charles R Greathouse IV, May 22 2017
CROSSREFS
KEYWORD
nonn,more,changed
AUTHOR
Farideh Firoozbakht, Jul 27 2003
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
STATUS
approved