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 A080905 #10 Feb 24 2020 17:16:31
%S A080905 4,1,4,1,4,1,2,1,1,1,2,1,4,1,4,1,2,1,1,1,2,1,4,1,4,1,2,1,1,1,2,1,2,1,
%T A080905 1,2,1,1,2,1,2,1,1,1,2,1,4,1,4,1,2,1,1,1,2,1,4,1,4,1,2,1,1,1,2,1,2,1,
%U A080905 1,2,1,1,2,1,2,1,1,1,2,1,4,1,4,1,2,1,1,1,2,1,4,1,4,1,2,1,1,1,2
%N A080905 Sequence of run lengths in first differences of A080900.
%C A080905 Even after 400000 terms there is no clear pattern here.
%H A080905 Antti Karttunen, <a href="/A080905/b080905.txt">Table of n, a(n) for n = 1..102526</a>
%e A080905 A080900 begins 1, 6, 11, 16, 21, 19, 24, 29, 34, 39, 37, 42, 47, 52, 57, 55, 60, 65, ..., the differences are 5, 5, 5, 5, -2, 5, 5, 5, 5, -2, ... with runs of lengths 4, 1, 4, 1, ...
%o A080905 (PARI)
%o A080905 up_to = 20000;
%o A080905 A080905list(up_to_n) = { my(xs=Map(), v, d, ds=vector(up_to_n)); mapput(xs,1,1); v = 1; for(n=2,1+up_to_n, v += (d=if(mapisdefined(xs,n), -2, +5)); mapput(xs,v,n); ds[n-1] = d); my(runlens=List([]), rl=1); for(i=2,#ds,if(ds[i]==ds[i-1],rl++, listput(runlens,rl);rl=1)); Vec(runlens); };
%o A080905 v080905 = A080905list(up_to);
%o A080905 A080905(n) = v080905[n]; \\ _Antti Karttunen_, Feb 24 2020
%Y A080905 Cf. A080900, A080922, A080927.
%K A080905 nonn
%O A080905 1,1
%A A080905 _N. J. A. Sloane_, Apr 01 2003