A129335 a(n) = phi(n!!) where phi is the Euler totient function. In other words, a(n) = A000010(A006882(n)).

1, 1, 2, 4, 8, 16, 48, 128, 432, 1024, 4320, 12288, 51840, 147456, 777600, 2359296, 12441600, 42467328, 223948800, 849346560, 4702924800, 16986931200, 103464345600, 407686348800, 2586608640000, 9784472371200, 69838433280000

Offset: 1

Author

Leroy Quet, May 26 2007

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..808

Crossrefs

Cf. A000010, A006882, A048855.

Programs

Mathematica

Table[EulerPhi[n!! ], {n, 1, 30}] (* Stefan Steinerberger, May 30 2007 *)

Formula

If n>2 is prime, a(n) = (n-1)*a(n-2). If n=2*p, where p is odd prime, a(n)=(n-2)*a(n-2). Otherwise, a(n) = n*a(n-2). - Max Alekseyev, May 26 2007

Extensions

More terms from Stefan Steinerberger, May 30 2007