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 A080783 #9 Nov 21 2013 12:47:59
%S A080783 1,6,11,16,21,20,25,30,35,40,39,44,49,54,59,58,63,68,73,72,71,76,81,
%T A080783 86,85,90,95,100,105,104,109,114,119,124,123,128,133,138,137,136,141,
%U A080783 146,151,150,155,160,165,170,169,174,179,184,189,188,193,198
%N A080783 a(1)=1, a(n)=a(n-1)-1 if n is already in the sequence, a(n)=a(n-1)+5 otherwise.
%F A080783 Conjectured to be asymptotic to 3n as n -> infinity.
%t A080783 lst={1};i=2;Do[If[MemberQ[lst,i],AppendTo[lst,Last[lst]-1], AppendTo[ lst,Last[lst]+5]];i++,{60}];lst (* _Harvey P. Dale_, Aug 20 2011 *)
%Y A080783 Cf. A079357, A079354, A080782, A064437.
%K A080783 nonn
%O A080783 1,2
%A A080783 _Benoit Cloitre_, Mar 07 2003