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 A178911 #12 Aug 14 2019 12:53:54
%S A178911 1,6,120,198,3696,6240,32640,56160,1941408,3592200,8119800,15628032,
%T A178911 27125280,59032080,61788240,125859840,1635834720,2147450880,
%U A178911 3709081680,16328199552,26198072160,52344970080,52396088160,209584184160,210197601120,236223190200,237385437360
%N A178911 Perfex numbers: n = binary XOR of divisors of n.
%C A178911 a(17) > 1e9.
%C A178911 10^11 < a(24) <= 209584184160. a(25) <= 210197601120. - _Donovan Johnson_, Mar 12 2011
%C A178911 a(28) > 3*10^11. - _Giovanni Resta_, Aug 14 2019
%t A178911 lst = {}; k = 1; While[k < 10^9, If[ BitXor @@ Divisors@k == k, AppendTo[lst, k]; Print@k]; k++ ]; lst (* _Robert G. Wilson v_, Jun 27 2010 *)
%o A178911 (PARI) xigma(n)=local(ds,r);ds=divisors(n);for(k=1,#ds,r=bitxor(r,ds[k]));r
%o A178911 for(n=1,1000000000,if(xigma(n)==n,print1(n",")))
%Y A178911 Cf. A178910, A178909, A000396, A003987.
%K A178911 nonn,base
%O A178911 1,2
%A A178911 _Franklin T. Adams-Watters_, Jun 22 2010
%E A178911 a(17) from _Robert G. Wilson v_, Jul 30 2010
%E A178911 a(18)-a(23) from _Donovan Johnson_, Mar 12 2011
%E A178911 a(24)-a(27) from _Giovanni Resta_, Aug 14 2019