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 A004656 #29 Sep 08 2022 08:44:33
%S A004656 1,11,1001,11011,1010001,11110011,1011011001,100010001011,
%T A004656 1100110100001,100110011100011,1110011010101001,101011001111111011,
%U A004656 10000001101111110001,110000101001111010011,10010001111101101111001
%N A004656 Powers of 3 written in base 2.
%D A004656 S. Wolfram, A New Kind of Science, Wolfram Media, 2002, pp. 120 and 903.
%H A004656 Vincenzo Librandi, <a href="/A004656/b004656.txt">Table of n, a(n) for n = 0..640</a>
%t A004656 Table[ FromDigits[ IntegerDigits[3^n, 2]], {n, 0, 14}]
%o A004656 (PARI) a(n)=fromdigits(binary(3^n)) \\ _M. F. Hasler_, Jun 23 2018
%o A004656 (Magma) [Seqint(Intseq(3^n, 2)): n in [0..30]]; // _G. C. Greubel_, Sep 10 2018
%Y A004656 Cf. A000079, A004643, ..., A004655: powers of 2 written in base 10, 4, 5, ..., 16
%Y A004656 Cf. A000244, A004658, A004659, ... : powers of 3 written in base 10, 4, 5, ...
%K A004656 nonn,base,easy
%O A004656 0,2
%A A004656 _N. J. A. Sloane_