The CAS Registry Mumber 99602-21-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,9,6,0 and 2 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 99602-21: (7*9)+(6*9)+(5*6)+(4*0)+(3*2)+(2*2)+(1*1)=158 158 % 10 = 8 So 99602-21-8 is a valid CAS Registry Number.