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 A066973 #30 Dec 12 2023 08:28:59
%S A066973 1,2,8,24,72,240,960,2880,15360,69120,165888,912384,3041280,9123840,
%T A066973 34062336,127733760,479001600,1596672000,6386688000,22992076800,
%U A066973 102187008000,429185433600,1755758592000,6730407936000,28267713331200
%N A066973 a(n) = phi(binomial(2n, n)).
%H A066973 Harry J. Smith, <a href="/A066973/b066973.txt">Table of n, a(n) for n = 1..200</a>
%F A066973 a(n) = A000010(A000984(n)).
%p A066973 with(numtheory):with(combinat):a:=n->phi(binomial(2*n,n)): seq(a(n), n=1..25); # _Zerinvary Lajos_, Oct 05 2007
%t A066973 f[n_] := EulerPhi[Binomial[2n,n]]; Table[f[n], {n,100}] (* _Enrique Pérez Herrero_, Jan 31 2012 *)
%o A066973 (SageMath) [euler_phi(binomial(2*n,n))for n in range(1,26)] # _Zerinvary Lajos_, Jun 06 2009
%o A066973 (PARI) a(n) = eulerphi(binomial(2*n, n)); \\ _Harry J. Smith_, Apr 12 2010
%K A066973 nonn
%O A066973 1,2
%A A066973 _Benoit Cloitre_, Jan 26 2002