The CAS Registry Mumber 83516-81-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,3,5,1 and 6 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 83516-81: (7*8)+(6*3)+(5*5)+(4*1)+(3*6)+(2*8)+(1*1)=138 138 % 10 = 8 So 83516-81-8 is a valid CAS Registry Number.