OFFSET
1,1
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..1000
EXAMPLE
2 is in this sequence because (4^2 - 1)/(2^2 - 1) = 5.
MAPLE
A271842:=n->`if`((4^n-1) mod (n^2-1) = 0, n, NULL): seq(A271842(n), n=2..10^4); # Wesley Ivan Hurt, Apr 18 2016
MATHEMATICA
Select[Range[1, 100], IntegerQ[(4^# - 1)/(#^2 - 1)] &] (* G. C. Greubel, Apr 15 2016 *)
PROG
(Magma) [0] cat [n: n in [2..240000] | Denominator((4^n-1)/(n^2-1)) eq 1];
(PARI) is(n)=Mod(4, n^2-1)^n==1 \\ Charles R Greathouse IV, Apr 15 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Apr 15 2016
STATUS
approved