The CAS Registry Mumber 853-15-6 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 8,5 and 3 respectively; the second part has 2 digits, 1 and 5 respectively. Calculate Digit Verification of CAS Registry Number 853-15: (5*8)+(4*5)+(3*3)+(2*1)+(1*5)=76 76 % 10 = 6 So 853-15-6 is a valid CAS Registry Number.