The CAS Registry Mumber 91320-81-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,1,3,2 and 0 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 91320-81: (7*9)+(6*1)+(5*3)+(4*2)+(3*0)+(2*8)+(1*1)=109 109 % 10 = 9 So 91320-81-9 is a valid CAS Registry Number.