The CAS Registry Mumber 671-63-6 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 6,7 and 1 respectively; the second part has 2 digits, 6 and 3 respectively. Calculate Digit Verification of CAS Registry Number 671-63: (5*6)+(4*7)+(3*1)+(2*6)+(1*3)=76 76 % 10 = 6 So 671-63-6 is a valid CAS Registry Number.