%I #18 Sep 08 2022 08:46:15
%S 1,5,10,50,100,500,1000,5000,10000,50000,100000,500000,1000000,
%T 5000000,10000000,50000000,100000000,500000000,1000000000,5000000000,
%U 10000000000,50000000000,100000000000,500000000000,1000000000000,5000000000000,10000000000000
%N a(n) = 2^((n-1) mod 2)*5*10^floor((n-1)/2).
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,10).
%F G.f.: (1 + 5*x)/(1 - 10*x^2). - _Michael De Vlieger_, Jan 26 2016; amended by _Georg Fischer_, Apr 03 2019
%t Table[2^Mod[n-1, 2]*5*10^Floor[(n-1)/2], {n, 0, 30}] (* or *)
%t LinearRecurrence[{0, 10}, {1, 5, 10, 50}, 30] (* or *)
%t CoefficientList[Series[(1+5x)/(1-10 x^2), {x, 0, 30}], x] (* _Michael De Vlieger_, Jan 26 2016; amended for 1,5,... by _Georg Fischer_, Apr 03 2019 *)
%o (PARI) a(n)=2^((n-1)%2)*5*10^((n-1)\2) \\ _Georg Fischer_, Apr 03 2019
%o (Magma) I:=[1,5,10]; [n le 3 select I[n] else 10*Self(n-2): n in [1..30]]; // _Vincenzo Librandi_, Jan 26 2016
%K nonn,easy
%O 0,2
%A _M. F. Hasler_, Jan 26 2016