%I #35 Sep 08 2022 08:44:33
%S 1,2,4,10,20,40,100,200,400,1000,2000,4000,10000,20000,40000,100000,
%T 200000,400000,1000000,2000000,4000000,10000000,20000000,40000000,
%U 100000000,200000000,400000000,1000000000
%N Powers of 2 written in base 8.
%C Or, numbers of form 10^n, 2*10^n, 4*10^n.
%C Or, numbers n such that the digits of n^3 are decreasing. - _Dmitry Kamenetsky_, Jun 15 2006
%H Vincenzo Librandi, <a href="/A004647/b004647.txt">Table of n, a(n) for n = 0..1000</a>
%H Thomas Harriot, <a href="http://echo.mpiwg-berlin.mpg.de/MPIWG:5PYT50NY">Manuscript 6782</a>, <a href="http://echo.mpiwg-berlin.mpg.de/ECHOdocuView?tocMode=thumbs&url=/mpiwg/online/permanent/library/HSPGZ0AE/&viewMode=image&tocPN=1&searchPN=1&characterNormalization=reg&query=&queryType=">p. 1</a>, c. 1599.
%H D. Panario, M. Sahin, and Q. Wang, <a href="http://www.emis.de/journals/INTEGERS/papers/n78/n78.Abstract.html">A family of Fibonacci-like conditional sequences</a>, INTEGERS, Vol. 13, 2013, #A78.
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,10).
%F a(0)=1, a(1)=2, a(2)=4, a(n)=10*a(n-3). - _Harvey P. Dale_, Aug 16 2012
%F G.f.: (1 + 2*x + 4*x^2)/(1 - 10*x^3 ). - _R. J. Mathar_, Mar 13 2015
%t Table[FromDigits[IntegerDigits[2^n,8]],{n,0,30}] (* or *) LinearRecurrence[ {0,0,10},{1,2,4},30] (* _Harvey P. Dale_, Aug 16 2012 *)
%o (PARI) a(n)=2^(n%3)*10^(n\3) \\ _Charles R Greathouse IV_, Oct 22 2014
%o (Magma) [Seqint(Intseq(2^n, 8)): n in [0..30]]; // _G. C. Greubel_, Sep 10 2018
%o (Python)
%o def A004647(n): return int(oct(2**n)[2:]) # _Chai Wah Wu_, May 23 2022
%K nonn,base,easy
%O 0,2
%A _N. J. A. Sloane_
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