The CAS Registry Mumber 79820-57-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,9,8,2 and 0 respectively; the second part has 2 digits, 5 and 7 respectively. Calculate Digit Verification of CAS Registry Number 79820-57: (7*7)+(6*9)+(5*8)+(4*2)+(3*0)+(2*5)+(1*7)=168 168 % 10 = 8 So 79820-57-8 is a valid CAS Registry Number.