The CAS Registry Mumber 83813-57-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,3,8,1 and 3 respectively; the second part has 2 digits, 5 and 7 respectively. Calculate Digit Verification of CAS Registry Number 83813-57: (7*8)+(6*3)+(5*8)+(4*1)+(3*3)+(2*5)+(1*7)=144 144 % 10 = 4 So 83813-57-4 is a valid CAS Registry Number.