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 A199397 #24 Nov 04 2015 14:21:36
%S A199397 1,2,11,16,65,178,619,2784,4929,24482,47371,133872,659713,1196754,
%T A199397 5945771,8408000,34643073,94509378,313886731,1475558352,2552700993,
%U A199397 12739900146,24581737195,70102639264,350315469377,639249412322,3139708751627,4623469310128,18666316402561
%N A199397 Binary XOR of 3^k as k varies from 0 to n.
%C A199397 Appears to be a self-convolution of an integer sequence (true for at least the initial 761 terms).
%H A199397 Paul D. Hanna, <a href="/A199397/b199397.txt">Table of n, a(n) for n = 0..300</a>
%e A199397 a(2) = 1 XOR 3 = 2; a(3) = 1 XOR 3 XOR 9 = 11; a(4) = 1 XOR 3 XOR 9 XOR 27 = 16.
%p A199397 A[0]:= 1:
%p A199397 for n from 1 to 40 do
%p A199397 A[n]:= Bits:-Xor(A[n-1],3^n)
%p A199397 od:
%p A199397 seq(A[i],i=0..40); # _Robert Israel_, Nov 02 2015
%t A199397 FoldList[BitXor, 3^Range[0, 28]] (* _Vladimir Reshetnikov_, Nov 02 2015 *)
%o A199397 (PARI) {a(n)=if(n<0,0,bitxor(a(n-1),3^n))}
%Y A199397 Cf. A199396.
%K A199397 nonn,base
%O A199397 0,2
%A A199397 _Paul D. Hanna_, Nov 05 2011