The CAS Registry Mumber 3664-00-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,6,6 and 4 respectively; the second part has 2 digits, 0 and 0 respectively. Calculate Digit Verification of CAS Registry Number 3664-00: (6*3)+(5*6)+(4*6)+(3*4)+(2*0)+(1*0)=84 84 % 10 = 4 So 3664-00-4 is a valid CAS Registry Number.