The CAS Registry Mumber 91781-00-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,1,7,8 and 1 respectively; the second part has 2 digits, 0 and 0 respectively. Calculate Digit Verification of CAS Registry Number 91781-00: (7*9)+(6*1)+(5*7)+(4*8)+(3*1)+(2*0)+(1*0)=139 139 % 10 = 9 So 91781-00-9 is a valid CAS Registry Number.