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 A131928 #10 Jun 22 2017 12:09:06
%S A131928 0,1,4,16,96,288,1440,5760,23040,92160,552960,1658880,7299072,
%T A131928 36495360,109486080,510935040,2043740160,7664025600,28740096000,
%U A131928 114960384000,459841536000,1839366144000,8583708672000,38626689024000
%N A131928 a(n) = phi(binomial(2*n,n)*n).
%p A131928 with(numtheory):with(combinat):a:=n->phi(binomial(2*n,n)*n): seq(a(n), n=0..25);
%t A131928 Table[EulerPhi[Binomial[2n,n]n],{n,0,30}] (* _Harvey P. Dale_, Apr 15 2012 *)
%Y A131928 Cf. A000010, A005430 Apery numbers: n*C(2n, n).
%K A131928 nonn
%O A131928 0,3
%A A131928 _Zerinvary Lajos_, Oct 05 2007