The CAS Registry Mumber 99548-21-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,9,5,4 and 8 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 99548-21: (7*9)+(6*9)+(5*5)+(4*4)+(3*8)+(2*2)+(1*1)=187 187 % 10 = 7 So 99548-21-7 is a valid CAS Registry Number.