This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A137344 #6 Mar 03 2024 14:42:24
%S A137344 3,9,12,36,48,144,192,576,768,2304,3072,9216,12288,36864,49152,147456,
%T A137344 196608,589824,786432,2359296,3145728,9437184,12582912,37748736,
%U A137344 50331648,150994944,201326592,603979776,805306368,2415919104
%N A137344 a(n)=4a(n-2). Also 3*A084221.
%H A137344 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0, 4).
%t A137344 RecurrenceTable[{a[1]==3,a[2]==9,a[n]==4*a[n-2]},a,{n,30}] (* or *) LinearRecurrence[ {0,4},{3,9},30] (* _Harvey P. Dale_, Sep 20 2018 *)
%K A137344 nonn
%O A137344 0,1
%A A137344 _Paul Curtz_, Apr 21 2008
%E A137344 More terms from _Harvey P. Dale_, Sep 20 2018