The CAS Registry Mumber 7556-82-3 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,5,5 and 6 respectively; the second part has 2 digits, 8 and 2 respectively. Calculate Digit Verification of CAS Registry Number 7556-82: (6*7)+(5*5)+(4*5)+(3*6)+(2*8)+(1*2)=123 123 % 10 = 3 So 7556-82-3 is a valid CAS Registry Number.