The CAS Registry Mumber 3753-66-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,7,5 and 3 respectively; the second part has 2 digits, 6 and 6 respectively. Calculate Digit Verification of CAS Registry Number 3753-66: (6*3)+(5*7)+(4*5)+(3*3)+(2*6)+(1*6)=100 100 % 10 = 0 So 3753-66-0 is a valid CAS Registry Number.