The CAS Registry Mumber 3664-01-5 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 1 respectively. Calculate Digit Verification of CAS Registry Number 3664-01: (6*3)+(5*6)+(4*6)+(3*4)+(2*0)+(1*1)=85 85 % 10 = 5 So 3664-01-5 is a valid CAS Registry Number.