OFFSET
1,7
EXAMPLE
a(5)=mu(1)*phi(4)+mu(2)*phi(3)+mu(3)*phi(2)+mu(4)*phi(1) = 1*2 - 1*2 - 1*1 + 0*1 = -1.
MAPLE
with(numtheory); f:=n->add(phi(i)*mobius(n-i), i=1..n-1);
PROG
(PARI) a(n)=sum(i=1, n-1, moebius(i)*eulerphi(n-i)) \\ Charles R Greathouse IV, Feb 21 2013
CROSSREFS
KEYWORD
sign
AUTHOR
Reinhard Zumkeller, Oct 07 2005
EXTENSIONS
Corrected by N. J. A. Sloane, Mar 01 2006
STATUS
approved