The CAS Registry Mumber 6515-61-3 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 6,5,1 and 5 respectively; the second part has 2 digits, 6 and 1 respectively. Calculate Digit Verification of CAS Registry Number 6515-61: (6*6)+(5*5)+(4*1)+(3*5)+(2*6)+(1*1)=93 93 % 10 = 3 So 6515-61-3 is a valid CAS Registry Number.