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 A337420 #8 Aug 27 2020 08:58:50
%S A337420 1,1,-14,-7,1222,-14873,26196,3522955,-110841786,2088947819,
%T A337420 -15869398244,-823790768205,55262757020956,-2199333670723343,
%U A337420 65894251730104552,-1235877788883794355,-18904175519674543546,3743957841955101437667,-268850524243738610546292,14826380281246309472525851
%N A337420 a(n) = Sum_{k=0..n} (-n)^(n-k) * binomial(2*k,k) * binomial(2*n,2*k).
%t A337420 a[n_] := Sum[If[n == 0, Boole[n == k], (-n)^(n - k)] * Binomial[2*k, k] * Binomial[2*n, 2*k], {k, 0, n}]; Array[a, 20, 0] (* _Amiram Eldar_, Aug 27 2020 *)
%o A337420 (PARI) {a(n) = sum(k=0, n, (-n)^(n-k)*binomial(2*k, k)*binomial(2*n, 2*k))}
%Y A337420 Main diagonal of A337419.
%Y A337420 Cf. A337388.
%K A337420 sign
%O A337420 0,3
%A A337420 _Seiichi Manyama_, Aug 27 2020