O ( a b , c d )  Π ( a , b )   = ( n − 1 ) μ ( a ) I { a b = c d }     + ( n − 2 ) Π ( c , d ) ( μ ( c ) I { a = d }   + μ ( a ) I { b = c }    )        ( 64 )     MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8akY=wiFfYdH8Gipec8Eeeu0xXdbba9frFj0=OqFfea0dXdd9vqai=hGuQ8kuc9pgc9s8qqaq=dirpe0xb9q8qiLsFr0=vr0=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@8BDE@