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 A099887 #8 Jul 11 2015 01:04:14
%S A099887 1,3,2,9,10,8,27,18,24,16,81,74,88,64,80,243,162,232,176,240,160,729,
%T A099887 554,648,608,720,544,640,2187,2642,2168,2800,2192,2624,2144,2784,6561,
%U A099887 4394,7032,4864,6640,4448,6944,4928,6560,19683,21826,17512,24336,19472
%N A099887 XOR difference triangle of the powers of 3, read by rows.
%C A099887 Main diagonal is A099888, the XOR BINOMIAL transform of the powers of 3. See A099884 for the definition of XOR BINOMIAL transform and for the definition of the XOR difference triangle.
%F A099887 T(n, k) = SumXOR_{i=0..k} (C(k, i)mod 2)*3^i, where SumXOR is the analog of summation under the binary XOR operation and C(k, i)mod 2 = A047999(k, i).
%e A099887 Rows begin:
%e A099887 [1],
%e A099887 [3,2],
%e A099887 [9,10,8],
%e A099887 [27,18,24,16],
%e A099887 [81,74,88,64,80],
%e A099887 [243,162,232,176,240,160],
%e A099887 [729,554,648,608,720,544,640],
%e A099887 [2187,2642,2168,2800,2192,2624,2144,2784],
%e A099887 [6561,4394,7032,4864,6640,4448,6944,4928,6560],
%e A099887 [19683,21826,17512,24336,19472,21984,17536,24480,19680,21824],...
%o A099887 (PARI) T(n,k)=local(B);B=0;for(i=0,k,B=bitxor(B,binomial(k,i)%2*3^(n-i)));B
%Y A099887 Cf. A099884, A047999, A099888.
%K A099887 nonn,tabl
%O A099887 0,2
%A A099887 _Paul D. Hanna_, Oct 28 2004