The CAS Registry Mumber 1673-76-3 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,6,7 and 3 respectively; the second part has 2 digits, 7 and 6 respectively. Calculate Digit Verification of CAS Registry Number 1673-76: (6*1)+(5*6)+(4*7)+(3*3)+(2*7)+(1*6)=93 93 % 10 = 3 So 1673-76-3 is a valid CAS Registry Number.