This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A108487 #7 Mar 20 2023 17:06:05
%S A108487 1,10,110,1600,25100,395000,6201000,97280000,1526010000,23938500000,
%T A108487 375525100000,5890896000000,92411011000000,1449659710000000,
%U A108487 22740940010000000,356739136000000000,5596198360100000000
%N A108487 Sum binomial(2n-2k,2k)10^(n-k), k=0..floor(n/2).
%C A108487 In general, sum{k=0..floor(n/2), C(2n-2k,2k)a^k*b^(n-k)} has expansion (1-bx-abx^2)/(1-2bx-(2ab-b^2)x^2-2ab^2*x^3+(ab)^2*x^4).
%H A108487 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (20,-80,200,-100).
%F A108487 G.f.: (1-10x-10x^2)/(1-20x-80x^2-200x^3+100x^4); a(n)=20a(n-1)+80a(n-2)+200a(n-3)-100a(n-4).
%t A108487 Table[Sum[Binomial[2n-2k,2k]10^(n-k),{k,0,Floor[n/2]}],{n,0,30}] (* or *) LinearRecurrence[{20,-80,200,-100},{1,10,110,1600},30] (* _Harvey P. Dale_, Mar 20 2023 *)
%K A108487 easy,nonn
%O A108487 0,2
%A A108487 _Paul Barry_, Jun 04 2005