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 A303671 #11 Apr 29 2018 13:00:11
%S A303671 1,-2,-4,-20,-140,-1192,-11656,-127072,-1517480,-19624400,-272656064,
%T A303671 -4046157472,-63844717184,-1067307017600,-18846094327360,
%U A303671 -350578477836160,-6854465726916640,-140564170444594880,-3017526392523529600,-67690323794750627200
%N A303671 a(n) = [x^n] (6 / Sum_{k=0..n} (k+3)!*x^k)^(1/2).
%H A303671 Seiichi Manyama, <a href="/A303671/b303671.txt">Table of n, a(n) for n = 0..446</a>
%p A303671 [seq(coeff(series((factorial(3)/add(factorial(k+3)*x^k,k=0..n))^(1/2), x,30),x,n),n=0..25)]; # _Muniru A Asiru_, Apr 29 2018
%o A303671 (PARI) N=66; x='x+O('x^N); Vec((3!/sum(k=0, N, (k+3)!*x^k))^(1/2))
%Y A303671 Cf. A077607, A303672, A303673.
%K A303671 sign
%O A303671 0,2
%A A303671 _Seiichi Manyama_, Apr 28 2018