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 A110044 #12 Aug 17 2017 22:33:01
%S A110044 11,23,12,11,1,10,9,1,8,7,1,6,5,1,4,3,1,2,1,1,0,1,1,0,1,1,0,1,1,0,1,1,
%T A110044 0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,
%U A110044 1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1,1,0,1
%N A110044 a(0) = 11, a(1) = 23; for n > 1, a(n) = |a(n-1) - a(n-2)|.
%C A110044 Since a(18)=a(19)=1, starting from here the sequence is periodic with period 3: 1,1,0,1,1,0,1,1,0,... - _Emeric Deutsch_, Jul 13 2005
%H A110044 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 1).
%F A110044 a(n) = 2/3 + 1/3*cos(2*Pi*n/3) + 1/3*3^(1/2)*sin(2*Pi*n/3) for n >= 19. - _Richard Choulet_, Dec 12 2008
%p A110044 a[0]:=11: a[1]:=23: for n from 2 to 120 do a[n]:=abs(a[n-1]-a[n-2]) od: seq(a[n],n=0..120); # _Emeric Deutsch_, Jul 13 2005
%t A110044 Join[{11, 23, 12, 11, 1, 10, 9, 1, 8, 7, 1, 6, 5, 1, 4, 3, 1, 2},LinearRecurrence[{0, 0, 1},{1, 1, 0},85]] (* _Ray Chandler_, Aug 25 2015 *)
%Y A110044 Cf. A141571.
%K A110044 nonn,easy
%O A110044 0,1
%A A110044 _Edwin F. Sampang_, Jul 09 2005
%E A110044 More terms from _Emeric Deutsch_, Jul 13 2005