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 A169967 #27 Jan 26 2020 21:02:39
%S A169967 0,4,40,44,400,404,440,444,4000,4004,4040,4044,4400,4404,4440,4444,
%T A169967 40000,40004,40040,40044,40400,40404,40440,40444,44000,44004,44040,
%U A169967 44044,44400,44404,44440,44444,400000,400004,400040,400044,400400,400404,400440,400444
%N A169967 Numbers whose decimal expansion contains only 0's and 4's.
%H A169967 Reinhard Zumkeller, <a href="/A169967/b169967.txt">Table of n, a(n) for n = 1..10000</a>
%H A169967 <a href="/index/Ar#10-automatic">Index entries for 10-automatic sequences</a>.
%F A169967 a(n+1) = Sum_{k>=0} A030308(n,k)*A093141(k+1). - _Philippe Deléham_, Oct 16 2011
%F A169967 a(n) = 4 * A007088(n-1).
%t A169967 FromDigits/@Tuples[{0,4},6] (* _Harvey P. Dale_, Dec 21 2018 *)
%o A169967 (PARI) print1(0);for(d=1,5,for(n=2^(d-1),2^d-1,print1(", ");forstep(i=d-1,0,-1,print1((n>>i)%2*4)))) \\ _Charles R Greathouse IV_, Nov 16 2011
%o A169967 (Haskell)
%o A169967 a169967 n = a169967_list !! (n-1)
%o A169967 a169967_list = map (* 4) a007088_list
%o A169967 -- _Reinhard Zumkeller_, Jan 10 2012
%Y A169967 Cf. A007088, A014263, A093141, A169964, A169965, A169966, A078243, A204093, A204094, A204095, A097256.
%K A169967 nonn,base,easy
%O A169967 1,2
%A A169967 _N. J. A. Sloane_, Aug 07 2010