%I #22 Sep 13 2024 00:39:27
%S 3,3,12,12,48,48,192,192,768,768,3072,3072,12288,12288,49152,49152,
%T 196608,196608,786432,786432,3145728,3145728,12582912,12582912,
%U 50331648,50331648,201326592,201326592,805306368,805306368,3221225472,3221225472,12884901888
%N Number of palindromes of length n (in base 4).
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,4).
%F a(n) = 3*4^floor((n-1)/2).
%F From _Colin Barker_, Feb 15 2013: (Start)
%F a(n) = 4*a(n-2).
%F G.f.: -3*x*(x+1) / ((2*x-1)*(2*x+1)). (End)
%t NestList[4#&,{3,3},20]//Flatten (* _Harvey P. Dale_, Dec 19 2016 *)
%Y Cf. A050683.
%K nonn,base,easy
%O 1,1
%A _Martin Renner_, May 02 2006
%E More terms from _Colin Barker_, Feb 15 2013