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%I #27 Sep 08 2022 08:44:33
%S 1,2,10,20,100,200,1000,2000,10000,20000,100000,200000,1000000,
%T 2000000,10000000,20000000,100000000,200000000,1000000000,2000000000,
%U 10000000000,20000000000,100000000000,200000000000
%N Powers of 2 written in base 4.
%C Also seems to be numbers k such that the digits of k^3 are cubes. - _Colin Barker_, Apr 21 2017
%H Vincenzo Librandi, <a href="/A004643/b004643.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,10).
%F From _Chai Wah Wu_, Sep 03 2020: (Start)
%F a(n) = 10*a(n-2) for n > 1.
%F G.f.: (-2*x - 1)/(10*x^2 - 1). (End)
%F a(n) = (3-(-1)^n)/2 * 10^floor(n/2). - _Bernard Schott_, Sep 17 2020
%t Table[FromDigits[IntegerDigits[2^n, 4]], {n, 0, 40}] (* _Vincenzo Librandi_, Jun 07 2013 *)
%t Table[{1,2}10^n,{n,0,20}]//Flatten (* _Harvey P. Dale_, Feb 14 2018 *)
%o (PARI) for(n=0,30, print1(fromdigits(digits(2^n, 4)), ", ")) \\ _G. C. Greubel_, Sep 10 2018
%o (Magma) [Seqint(Intseq(2^n, 4)): n in [0..30]]; // _G. C. Greubel_, Sep 10 2018
%K nonn,base,easy
%O 0,2
%A _N. J. A. Sloane_
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