The CAS Registry Mumber 81102-51-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,1,1,0 and 2 respectively; the second part has 2 digits, 5 and 1 respectively. Calculate Digit Verification of CAS Registry Number 81102-51: (7*8)+(6*1)+(5*1)+(4*0)+(3*2)+(2*5)+(1*1)=84 84 % 10 = 4 So 81102-51-4 is a valid CAS Registry Number.