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 A093143 Expansion of (1-5*x)/(1-10*x). 12

%I

%S 1,5,50,500,5000,50000,500000,5000000,50000000,500000000,5000000000,

%T 50000000000,500000000000,5000000000000,50000000000000,

%U 500000000000000,5000000000000000,50000000000000000,500000000000000000

%N Expansion of (1-5*x)/(1-10*x).

%C Partial sums are A093142. A convex combination of 10^n and 0^n.

%C a(n) is the number of compositions of even natural numbers in n parts <= 9 (0 is counted as a part); also the number of ways of placing of an even number of indistinguishable objects into n distinguishable boxes with the condition that at most 9 objects can be placed in each box. - _Adi Dani_, May 17 2011

%C See an A246057 comment with a reference for the k-family satisfying a so-called curious cubic identity involving A246057(k-1), a(k) and A002277(k). - _Wolfdieter Lang_, Feb 07 2017

%H <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (10).

%F a(n) = 5*10^n/10 for n>0.

%F a(n) = Sum_{k=0..n} A134309(n,k)*5^k = Sum_{k=0..n} A055372(n,k)*4^k. - _Philippe DelĂ©ham_, Feb 04 2012

%e From _Adi Dani_, May 17 2011: (Start)

%e a(2)=50: there are 50 compositions of even numbers into 2 parts <= 9:

%e (0,0);

%e (0,2),(2,0),(1,1);

%e (0,4),(4,0),(1,3),(3,1),(2,2);

%e (0,6),(6,0),(1,5),(5,1),(2,4),(4,2),(3,3);

%e (0,8),(8,0),(1,7),(7,1),(2,6),(6,2),(3,5),(5,3),(4,4);

%e (1,9),(9,1),(2,8),(8,2),(3,7),(7,3),(4,6),(6,4),(5,5);

%e (3,9),(9,3),(4,8),(8,4),(5,7),(7,5),(6,6);

%e (5,9),(9,5),(6,8),(8,6),(7,7);

%e (7,9),(9,7),(8,8);

%e (9,9).

%e (End)

%e Curious cubic identities (see a comment above): 1^3 + 5^3 + 3^3 = 153, 16^3 + 50^3 + 33^3 = 165033, 166^3 + 500^3 + 333^3 = 166500333, ... - _Wolfdieter Lang_, Feb 07 2017

%t Table[Ceiling[1/2*10^n],{n,0,30}] (* _Adi Dani_, Jun 20 2011 *)

%o (PARI) Vec((1-5*x)/(1-10*x) + O(x^100)) \\ _Altug Alkan_, Nov 01 2015

%Y Cf. A002277, A246057.

%K nonn,easy

%O 0,2

%A _Paul Barry_, Mar 24 2004

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Last modified February 22 05:49 EST 2019. Contains 320385 sequences. (Running on oeis4.)