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 A337465 #13 Apr 29 2021 04:32:46
%S A337465 1,5,-6,-139,1654,-5853,-196860,6258751,-112580442,985287863,
%T A337465 26443436876,-1897380617625,72596047613116,-2086036395460171,
%U A337465 39493340495025864,304974352009838745,-85532651616832374010,6040114369000387188975,-321378391411642082323524,14224299551865677212271567
%N A337465 a(n) = Sum_{k=0..n} (-n)^(n-k) * binomial(2*k,k) * binomial(2*n+1,2*k).
%t A337465 a[n_] := Sum[If[n == n - k == 0, 1, (-n)^(n-k)] * Binomial[2*k, k] * Binomial[2*n+1, 2*k], {k, 0, n}]; Array[a, 20, 0] (* _Amiram Eldar_, Apr 29 2021 *)
%o A337465 (PARI) {a(n) = sum(k=0, n, (-n)^(n-k)*binomial(2*k, k)*binomial(2*n+1, 2*k))}
%Y A337465 Main diagonal of A337464.
%Y A337465 Cf. A337387, A337420.
%K A337465 sign
%O A337465 0,2
%A A337465 _Seiichi Manyama_, Aug 28 2020