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 A154805 #27 Jul 03 2021 10:58:28
%S A154805 1111,11110000,111100001111,1111000011110000,11110000111100001111,
%T A154805 111100001111000011110000,1111000011110000111100001111,
%U A154805 11110000111100001111000011110000,111100001111000011110000111100001111
%N A154805 Numbers with 4n binary digits where every run length is 4, written in binary.
%C A154805 A154806 written in base 2.
%H A154805 Vincenzo Librandi, <a href="/A154805/b154805.txt">Table of n, a(n) for n = 1..100</a>
%H A154805 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (10000,1,-10000).
%F A154805 From _Colin Barker_, Apr 20 2014: (Start)
%F A154805 a(n) = (-10001-9999*(-1)^n+2^(5+4*n)*625^(1+n))/180018.
%F A154805 a(n) = 10000*a(n-1)+a(n-2)-10000*a(n-3).
%F A154805 G.f.: 1111*x / ((x-1)*(x+1)*(10000*x-1)). (End)
%e A154805 n ... a(n) ................... A154806(n)
%e A154805 1 ... 1111 ................... 15
%e A154805 2 ... 11110000 ............... 240
%e A154805 3 ... 111100001111 ........... 3855
%e A154805 4 ... 1111000011110000 ....... 61680
%e A154805 5 ... 11110000111100001111 ... 986895
%t A154805 CoefficientList[Series[1111/((x - 1) (x + 1) (10000 x - 1)), {x, 0, 10}], x] (* _Vincenzo Librandi_, Apr 22 2014 *)
%t A154805 LinearRecurrence[{10000,1,-10000},{1111,11110000,111100001111},20] (* _Harvey P. Dale_, Jul 31 2017 *)
%o A154805 (PARI) Vec(1111*x/((x-1)*(x+1)*(10000*x-1)) + O(x^100)) \\ _Colin Barker_, Apr 20 2014
%Y A154805 Cf. A152775, A153435, A154806, A154807.
%K A154805 easy,nonn,base
%O A154805 1,1
%A A154805 _Omar E. Pol_, Jan 25 2009