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 A210680 #19 Nov 27 2014 13:11:48
%S A210680 0,1,3,8,27,89,272,873,2859,8936,25491,67665,228192,752241,2167859,
%T A210680 6833896,18464907,52758345,142005584,440498361,1186119547,3461957320,
%U A210680 9357060899,26968655777,72945663424,226371206881,613739200867,1752444795592,4702791627067,14623717009785
%N A210680 a(n) = (3*a(n-1)) XOR a(n-2).
%H A210680 Harvey P. Dale, <a href="/A210680/b210680.txt">Table of n, a(n) for n = 0..1000</a>
%F A210680 a(n) = (3*a(n-1)) XOR a(n-2), a(0)=0, a(1)=1.
%t A210680 RecurrenceTable[{a[0]==0,a[1]==1,a[n]==BitXor[3a[n-1],a[n-2]]},a,{n,30}] (* _Harvey P. Dale_, Nov 27 2014 *)
%Y A210680 Cf. A168081: a(n) = (2*a(n-1)) XOR a(n-2), a(0)=0, a(1)=1.
%Y A210680 Cf. A101624: a(n) = (2*a(n-2)) XOR a(n-1), a(0)=0, a(1)=1.
%Y A210680 Cf. A204771: a(n) = (3*a(n-2)) XOR a(n-1), a(0)=0, a(1)=1.
%K A210680 nonn,base,easy
%O A210680 0,3
%A A210680 _Alex Ratushnyak_, May 09 2012