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 A307158 #20 May 20 2021 04:44:29
%S A307158 1,1,1,0,-15,-99,-398,-1175,-2351,0,29601,183195,756978,2351805,
%T A307158 4885791,0,-63746991,-400000275,-1675991918,-5274560891,-11081420615,
%U A307158 0,147257373891,931226954949,3929550225586,12446852889901,26304183607651,0,-353181028924809
%N A307158 a(n) = Sum_{k=0..floor(n/3)} (-1)^k * binomial(n,3*k)^2.
%H A307158 Seiichi Manyama, <a href="/A307158/b307158.txt">Table of n, a(n) for n = 0..1752</a>
%F A307158 a(6*n+3) = 0 for n >= 0.
%t A307158 a[n_] := Sum[(-1)^k * Binomial[n,3*k]^2, {k, 0, Floor[n/3]}]; Array[a, 30, 0] (* _Amiram Eldar_, May 20 2021 *)
%o A307158 (PARI) {a(n) = sum(k=0, n\3, (-1)^k*binomial(n, 3*k)^2)}
%Y A307158 Central coefficients of number triangle A307156.
%Y A307158 Cf. A057681, A119363, A307091.
%K A307158 sign
%O A307158 0,5
%A A307158 _Seiichi Manyama_, Mar 27 2019