A131928 - OEIS

%I #10 Jun 22 2017 12:09:06

%S 0,1,4,16,96,288,1440,5760,23040,92160,552960,1658880,7299072,

%T 36495360,109486080,510935040,2043740160,7664025600,28740096000,

%U 114960384000,459841536000,1839366144000,8583708672000,38626689024000

%N a(n) = phi(binomial(2*n,n)*n).

%p with(numtheory):with(combinat):a:=n->phi(binomial(2*n,n)*n): seq(a(n), n=0..25);

%t Table[EulerPhi[Binomial[2n,n]n],{n,0,30}] (* _Harvey P. Dale_, Apr 15 2012 *)

%Y Cf. A000010, A005430 Apery numbers: n*C(2n, n).

%K nonn

%O 0,3

%A _Zerinvary Lajos_, Oct 05 2007