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 A156872 #15 Dec 12 2023 08:07:33
%S A156872 1,3,-1,3,1,0,-1,-3,1,-3,-1,0,1,3,-1,3,1,0,-1,-3,1,-3,-1,0,1,3,-1,3,1,
%T A156872 0,-1,-3,1,-3,-1,0,1,3,-1,3,1,0,-1,-3,1,-3,-1,0,1,3,-1,3,1,0,-1,-3,1,
%U A156872 -3,-1,0
%N A156872 Period 12: 1,3,-1,3,1,0,-1,-3,1,-3,-1,0 repeated.
%C A156872 First differences of A154811.
%H A156872 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,-1).
%F A156872 Palindromic properties: a(n+6)= -a(n). a(12k+i)=a(12k+4-i), i=0..2. a(12k+5+i)=a(12k+11-i), i=0..3.
%F A156872 a(n) = A156194(n+1)-A156194(n+7) = A156194(n+1)-A156199(n+1).
%F A156872 a(n) = A156227(n+1) (mod 9).
%F A156872 a(n+1) -a(n)= A156346(n+1).
%F A156872 a(n)=A056594(n)+3*A014021(n-1). G.f.: (1+3*x-x^2+3*x^3+x^4)/((1+x^2)*(x^4-x^2+1)). - _R. J. Mathar_, Feb 23 2009
%t A156872 PadRight[{},70,{1,3,-1,3,1,0,-1,-3,1,-3,-1,0}] (* _Harvey P. Dale_, Sep 23 2012 *)
%K A156872 sign,easy,less
%O A156872 0,2
%A A156872 _Paul Curtz_, Feb 17 2009
%E A156872 Edited, formulas commenting other sequences removed, by _R. J. Mathar_, Feb 23 2009