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 A169811 #13 Jul 08 2019 12:21:25
%S A169811 0,0,1,5,14,10,19,27,44,36,61,73,66,86,103,119,152,136,185,173,198,
%T A169811 242,235,259,308,348,325,353,394,430,463,495,560,528,625,597,702,666,
%U A169811 707,811,796,884,941,921,1010,1062,1047,1095,1192,1272,1225,1309,1366,1442,1531
%N A169811 a(n) = n XOR n*(n+1)/2.
%H A169811 Amiram Eldar, <a href="/A169811/b169811.txt">Table of n, a(n) for n = 0..10000</a>
%t A169811 Table[BitXor[n (n + 1)/2, n], {n, 0, 100}] (* _Vladimir Joseph Stephan Orlovsky_, Jul 17 2011 *)
%o A169811 (PARI) a(n)=bitxor(n, n*(n+1)/2); \\ _Michel Marcus_, Jul 08 2019
%Y A169811 Cf. A000217, A070883, A169810.
%K A169811 nonn
%O A169811 0,4
%A A169811 _N. J. A. Sloane_, May 28 2010