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%I #18 Apr 01 2018 09:29:18
%S 1,4,40,400,4000,40000,400000,4000000,40000000,400000000,4000000000,
%T 40000000000,400000000000,4000000000000,40000000000000,
%U 400000000000000,4000000000000000,40000000000000000,400000000000000000
%N Expansion of (1-6x)/(1-10x).
%C Partial sums are A093140. A convex combination of 10^n and 0^n.
%H <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (10).
%F a(n) = 4*10^n/10 + 6*0^n/10.
%F a(n) = phi(10^n). - _Paul Barry_, Jul 02 2007
%F a(n) = 4*10^(n-1), n>0. - _Vincenzo Librandi_, Aug 02 2010
%t Table[EulerPhi[10^n],{n,0,40}] (* _Vladimir Joseph Stephan Orlovsky_, Nov 10 2009 *)
%t Join[{1},NestList[10#&,4,20]] (* _Harvey P. Dale_, Apr 01 2018 *)
%o (PARI) Vec((1-6*x)/(1-10*x) + O(x^30)) \\ _Michel Marcus_, Jan 17 2015
%K easy,nonn
%O 0,2
%A _Paul Barry_, Mar 24 2004
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