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 A046673 #14 Mar 08 2020 00:24:12
%S A046673 2,36,1320,84000,8285760,1173553920,226040855040,56865153945600,
%T A046673 18112111963545600,7125892746964992000,3394344333441245184000,
%U A046673 1925382105537337294848000,1282520788685931213619200000,991363455147400701817651200000,880169729965718014490443776000000
%N A046673 a(n) = (2n)!*Sum_{i=1..n} 1/i.
%H A046673 I. Nemes et al., <a href="https://www.jstor.org/stable/2975078">How to do Monthly problems with your computer</a>, Amer. Math. Monthly, 104 (1997), 505-519.
%t A046673 Table[(2n)!HarmonicNumber[n],{n,20}] (* _Harvey P. Dale_, Sep 27 2013 *)
%o A046673 (PARI) a(n) = (2*n)!*sum(k=1, n, 1/k); \\ _Michel Marcus_, Jul 11 2018
%Y A046673 Cf. A000254, A101613.
%K A046673 nonn
%O A046673 1,1
%A A046673 _N. J. A. Sloane_