A066973 a(n) = phi(binomial(2n, n)).

1, 2, 8, 24, 72, 240, 960, 2880, 15360, 69120, 165888, 912384, 3041280, 9123840, 34062336, 127733760, 479001600, 1596672000, 6386688000, 22992076800, 102187008000, 429185433600, 1755758592000, 6730407936000, 28267713331200

Offset: 1

Author

Benoit Cloitre, Jan 26 2002

Keywords

• nonn

Links

• Harry J. Smith, Table of n, a(n) for n = 1..200

Programs

Maple

with(numtheory):with(combinat):a:=n->phi(binomial(2*n,n)): seq(a(n), n=1..25); # Zerinvary Lajos, Oct 05 2007

Mathematica

f[n_] := EulerPhi[Binomial[2n,n]]; Table[f[n], {n,100}] (* Enrique Pérez Herrero, Jan 31 2012 *)

PARI

a(n) = eulerphi(binomial(2*n, n)); \\ Harry J. Smith, Apr 12 2010

SageMath

[euler_phi(binomial(2*n,n))for n in range(1,26)] # Zerinvary Lajos, Jun 06 2009

Formula

a(n) = A000010(A000984(n)).