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 A371870 #11 Apr 25 2024 13:22:57
%S A371870 1,1,4,14,51,189,709,2683,10220,39130,150438,580328,2245004,8705686,
%T A371870 33828704,131688362,513445147,2004688605,7836832057,30670416703,
%U A371870 120153739079,471143251989,1848978071615,7261781367389,28540427527441,112243216215879,441693646453729
%N A371870 a(n) = Sum_{k=0..floor(n/2)} binomial(2*n-k-1,n-2*k).
%F A371870 a(n) = [x^n] 1/((1-x-x^2) * (1-x)^(n-1)).
%F A371870 a(n) ~ 4^n / sqrt(Pi*n). - _Vaclav Kotesovec_, Apr 16 2024
%F A371870 a(n) = A354267(2*n, n). - _Peter Luschny_, Apr 25 2024
%o A371870 (PARI) a(n) = sum(k=0, n\2, binomial(2*n-k-1, n-2*k));
%Y A371870 Cf. A072547, A114121, A354267.
%K A371870 nonn
%O A371870 0,3
%A A371870 _Seiichi Manyama_, Apr 10 2024