The CAS Registry Mumber 91633-80-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,1,6,3 and 3 respectively; the second part has 2 digits, 8 and 0 respectively. Calculate Digit Verification of CAS Registry Number 91633-80: (7*9)+(6*1)+(5*6)+(4*3)+(3*3)+(2*8)+(1*0)=136 136 % 10 = 6 So 91633-80-6 is a valid CAS Registry Number.