The CAS Registry Mumber 99441-21-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,9,4,4 and 1 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 99441-21: (7*9)+(6*9)+(5*4)+(4*4)+(3*1)+(2*2)+(1*1)=161 161 % 10 = 1 So 99441-21-1 is a valid CAS Registry Number.