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 A375021 #26 Aug 09 2024 10:07:47
%S A375021 1,1,0,-3,-7,-6,11,49,78,3,-297,-750,-691,1271,5970,9877,647,-38640,
%T A375021 -100381,-95689,170394,827453,1398933,131418,-5472241,-14495327,
%U A375021 -14186826,24241947,121177521,208360152,25541493,-807963639,-2175698844,-2179521039
%N A375021 Expansion of 1/sqrt(1 - 2*x + 3*x^2 + 2*x^3 + x^4).
%F A375021 n * a(n) = (2*n-1)*a(n-1) - 3*(n-1)*a(n-2) - (2*n-3)*a(n-3) - (n-2)*a(n-4).
%F A375021 a(n) = Sum_{k=0..floor(n/2)} (-1)^k * binomial(n-k,k)^2.
%o A375021 (PARI) my(N=40, x='x+O('x^N)); Vec(1/sqrt(1-2*x+3*x^2+2*x^3+x^4))
%o A375021 (PARI) a(n) = sum(k=0, n\2, (-1)^k*binomial(n-k, k)^2);
%Y A375021 Cf. A051286, A108488, A108489.
%K A375021 sign
%O A375021 0,4
%A A375021 _Seiichi Manyama_, Aug 09 2024