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 A126804 #48 Sep 08 2022 08:45:29
%S A126804 2,24,360,6720,151200,3991680,121080960,4151347200,158789030400,
%T A126804 6704425728000,309744468633600,15543540607795200,841941782922240000,
%U A126804 48962152914554880000,3042648073975910400000,201220459292273541120000,14110584707870682071040000
%N A126804 a(n) = (2n)! / (n-1)!.
%C A126804 Old name was "Multiplying n X n integers above n".
%C A126804 a(n) = 2*A001814(n). - _Zerinvary Lajos_, May 03 2007
%C A126804 A179214(n) <= a(n). - _Reinhard Zumkeller_, Jul 05 2010
%C A126804 Product of the numbers from n to 2n. - _Wesley Ivan Hurt_, Dec 14 2015
%H A126804 Robert Israel, <a href="/A126804/b126804.txt">Table of n, a(n) for n = 1..360</a>
%H A126804 Elliot J. Carr and Matthew J. Simpson, <a href="https://arxiv.org/abs/1707.06331">Accurate and efficient calculation of finite response times for groundwater flow</a>, arXiv:1707.06331 [physics.flu-dyn], 2017, p. 11.
%F A126804 a(n) = (2n)! / (n-1)!.
%F A126804 a(n) = Product_{i=n..2n} i. - _Wesley Ivan Hurt_, Dec 14 2015
%F A126804 From _Robert Israel_, Dec 15 2015: (Start)
%F A126804 a(n) = (2*n*(2*n-1)/(n-1))*a(n-1).
%F A126804 E.g.f.: 2*x/(1-4*x)^(3/2). (End)
%F A126804 a(n) = Pochhammer(n,n+1). - _Pedro Caceres_, Mar 10 2018
%e A126804 a(5) = 151200 because five digits above 5: (6, 7, 8, 9, 10), multiplied by five equals 5*(6*7*8*9*10) = 151200.
%p A126804 a:=n->sum((count(Permutation(2*n+2),size=n+1)),j=0..n): seq(a(n), n=0..15); # _Zerinvary Lajos_, May 03 2007
%p A126804 seq(mul((n+k), k=0..n), n=1..16); # _Zerinvary Lajos_, Sep 21 2007
%p A126804 with(combstruct):with(combinat) :bin := {B=Union(Z,Prod(B,B))}: seq (count([B,bin,labeled],size=n)*(n-1), n=2..17); # _Zerinvary Lajos_, Dec 05 2007
%t A126804 Table[Pochhammer[n, n + 1], {n, 17}] (* _Arkadiusz Wesolowski_, Aug 13 2012 *)
%t A126804 Table[(2 n)!/(n - 1)!, {n, 20}] (* _Wesley Ivan Hurt_, Dec 14 2015 *)
%o A126804 (Magma) [Factorial(2*n)/Factorial(n-1) : n in [1..20]]; // _Wesley Ivan Hurt_, Dec 14 2015
%o A126804 (PARI) a(n) = prod(k=n, 2*n, k); \\ _Michel Marcus_, Dec 15 2015
%o A126804 (PARI) x='x+O('x^99); Vec(serlaplace(2*x/(1-4*x)^(3/2))) \\ _Altug Alkan_, Mar 11 2018
%Y A126804 Cf. A045943, A073838. - _Reinhard Zumkeller_, Jul 05 2010
%Y A126804 Cf. A001814, A179214.
%K A126804 easy,nonn
%O A126804 1,1
%A A126804 Jonathan R. Love (japanada11(AT)yahoo.ca), Feb 22 2007
%E A126804 New name from _Wesley Ivan Hurt_, Dec 15 2015