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 A200878 #26 Oct 11 2021 13:45:00
%S A200878 4,6,8,9,12,16,18,24,25,27,32,35,36,48,49,54,64,72,81,96,108,121,125,
%T A200878 128,143,144,162,169,175,192,216,243,245,256,288,289,323,324,343,361,
%U A200878 384,391,432,437,486,493,512,527,529,551,576,589,625,648,667,713
%N A200878 Composite numbers whose prime factors have equal numbers of bits.
%H A200878 Arkadiusz Wesolowski, <a href="/A200878/b200878.txt">Table of n, a(n) for n = 1..10000</a>
%e A200878 7429 = 17*19*23 -> 10001*10011*10111, therefore 7429 is a term.
%e A200878 7430 = 2*5*743 -> 10*101*1011100111, therefore 7430 is not a term.
%t A200878 lst = {}; Do[b = IntegerDigits[FactorInteger[n], 2]; If[! PrimeQ[n] && Length[b[[-1, 1]]] == Length[b[[1, 1]]], AppendTo[lst, n]], {n, 4, 6!}]; lst (* _Arkadiusz Wesolowski_, Dec 03 2011 *)
%t A200878 Select[Range[800],CompositeQ[#]&&Length[Union[IntegerLength[ #,2]&/@ FactorInteger[ #][[All,1]]]]==1&] (* _Harvey P. Dale_, Oct 11 2021 *)
%o A200878 (PARI) is(n)=my(f=factor(n)[,1]);#binary(f[1])==#binary(f[#f])&&!isprime(n) \\ _Charles R Greathouse IV_, Dec 23 2011
%Y A200878 Supersequence of A085721 and of A182302.
%K A200878 base,nonn
%O A200878 1,1
%A A200878 _Arkadiusz Wesolowski_, Nov 23 2011