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 A133259 #8 Nov 17 2022 05:14:21
%S A133259 1,2,3,6,5,4,7,8,9,12,11,10,13,14,15,18,17,16,19,20,21,24,23,22,25,26,
%T A133259 27,30,29,28,31,32,33,36,35,34,37,38,39,42,41,40,43,44,45,48,47,46,49,
%U A133259 50,51,54,53,52,55,56,57,60,59,58,61,62,63,66,65,64,67,68,69,72,71,70
%N A133259 a(6n) = 6n+1, a(6n+1) = 6n+2, a(6n+2) = 6n+3, a(6n+3) = 6n+6, a(6n+4) = 6n+5, a(6n+5) = 6n+4.
%H A133259 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (2, -2, 2, -2, 2, -1).
%t A133259 Table[6n+{1,2,3,6,5,4},{n,0,20}]//Flatten (* _Harvey P. Dale_, Sep 30 2016 *)
%K A133259 nonn,easy
%O A133259 0,2
%A A133259 _Paul Curtz_, Oct 15 2007