A268100 a(n) = 2^((n-1) mod 2)*5*10^floor((n-1)/2).

1, 5, 10, 50, 100, 500, 1000, 5000, 10000, 50000, 100000, 500000, 1000000, 5000000, 10000000, 50000000, 100000000, 500000000, 1000000000, 5000000000, 10000000000, 50000000000, 100000000000, 500000000000, 1000000000000, 5000000000000, 10000000000000

Offset

0,2

Links

Table of n, a(n) for n=0..26.

Index entries for linear recurrences with constant coefficients, signature (0,10).

Formula

G.f.: (1 + 5*x)/(1 - 10*x^2). - Michael De Vlieger, Jan 26 2016; amended by Georg Fischer, Apr 03 2019

Mathematica

Table[2^Mod[n-1, 2]*5*10^Floor[(n-1)/2], {n, 0, 30}] (* or *)
LinearRecurrence[{0, 10}, {1, 5, 10, 50}, 30] (* or *)
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 *)

Prog

(PARI) a(n)=2^((n-1)%2)*5*10^((n-1)\2) \\ Georg Fischer, Apr 03 2019
(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

Crossrefs

Sequence in context: A270100 A271287 A003587 * A205884 A032088 A081076

Adjacent sequences: A268097 A268098 A268099 * A268101 A268102 A268103

Keyword

nonn,easy

Author

M. F. Hasler, Jan 26 2016

Status

approved