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 A004655 #26 Jan 27 2023 10:15:21
%S A004655 1,2,4,8,10,20,40,80,100,200,400,800,1000,2000,4000,8000,10000,20000,
%T A004655 40000,80000,100000,200000,400000,800000,1000000,2000000,4000000,
%U A004655 8000000,10000000,20000000,40000000,80000000
%N A004655 Powers of 2 written in base 16.
%C A004655 10^(Floor[n/4]) | a(n). The first term of each value cycles the pattern {1, 2, 4, 8}. - _G. C. Greubel_, Sep 10 2018
%H A004655 G. C. Greubel, <a href="/A004655/b004655.txt">Table of n, a(n) for n = 0..2500</a>
%H A004655 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,10).
%F A004655 a(n) = 2^(n mod 4)*10^floor(n/4). - _M. F. Hasler_, Jun 22 2018
%F A004655 From _Chai Wah Wu_, Sep 03 2020: (Start)
%F A004655 a(n) = 10*a(n-4) for n > 3.
%F A004655 G.f.: -(2*x + 1)*(4*x^2 + 1)/(10*x^4 - 1). (End)
%t A004655 Table[FromDigits[IntegerDigits[2^n, 16]], {n, 50}] (* _G. C. Greubel_, Sep 11 2018 *)
%o A004655 (PARI) apply( a(n)=2^(n%4)*10^(n\4), [0..30]) \\ _M. F. Hasler_, Jun 22 2018
%o A004655 (Magma) [Seqint(Intseq(2^n, 16)): n in [0..30]]; // _G. C. Greubel_, Sep 10 2018
%o A004655 (Python)
%o A004655 def A004655(n): return 10**(n>>2)<<(n&3) # _Chai Wah Wu_, Jan 27 2023
%Y A004655 Cf. A000079, A004643, ..., A004654: powers of 2 written in base 10, 4, 5, ..., 15.
%Y A004655 Cf. A000244, A004656, A004658, A004659, ... : powers of 3 in base 10, 2, 4, 5, ...
%K A004655 nonn,base,easy
%O A004655 0,2
%A A004655 _N. J. A. Sloane_