The CAS Registry Mumber 98305-21-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,8,3,0 and 5 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 98305-21: (7*9)+(6*8)+(5*3)+(4*0)+(3*5)+(2*2)+(1*1)=146 146 % 10 = 6 So 98305-21-6 is a valid CAS Registry Number.