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 A169966 #33 Oct 30 2023 09:51:26
%S A169966 0,3,30,33,300,303,330,333,3000,3003,3030,3033,3300,3303,3330,3333,
%T A169966 30000,30003,30030,30033,30300,30303,30330,30333,33000,33003,33030,
%U A169966 33033,33300,33303,33330,33333,300000,300003,300030,300033,300300,300303,300330,300333
%N A169966 Numbers whose decimal expansion contains only 0's and 3's.
%H A169966 Reinhard Zumkeller, <a href="/A169966/b169966.txt">Table of n, a(n) for n = 1..10000</a>
%F A169966 a(n+1) = Sum_{k>=0} A030308(n,k)*A093138(k+1). - _Philippe Deléham_, Oct 16 2011
%F A169966 a(n) = 3 * A007088(n-1).
%t A169966 Map[FromDigits,Tuples[{0,3},6]] (* _Paolo Xausa_, Oct 30 2023 *)
%o A169966 (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*3)))) \\ _Charles R Greathouse IV_, Nov 16 2011
%o A169966 (Haskell)
%o A169966 a169966 n = a169966_list !! (n-1)
%o A169966 a169966_list = map (* 3) a007088_list
%o A169966 -- _Reinhard Zumkeller_, Jan 10 2012
%o A169966 (Python)
%o A169966 def a(n): return 3*int(bin(n)[2:])
%o A169966 print([a(n) for n in range(40)]) # _Michael S. Branicky_, Mar 30 2021
%Y A169966 Cf. A007088, A014263, A169964, A169965, A169967.
%Y A169966 Cf. A078242, A204093, A204094, A204095, A097256.
%K A169966 nonn,base,easy
%O A169966 1,2
%A A169966 _N. J. A. Sloane_, Aug 07 2010