The CAS Registry Mumber 91098-33-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,1,0,9 and 8 respectively; the second part has 2 digits, 3 and 3 respectively. Calculate Digit Verification of CAS Registry Number 91098-33: (7*9)+(6*1)+(5*0)+(4*9)+(3*8)+(2*3)+(1*3)=138 138 % 10 = 8 So 91098-33-8 is a valid CAS Registry Number.