The CAS Registry Mumber 81655-71-2 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,1,6,5 and 5 respectively; the second part has 2 digits, 7 and 1 respectively. Calculate Digit Verification of CAS Registry Number 81655-71: (7*8)+(6*1)+(5*6)+(4*5)+(3*5)+(2*7)+(1*1)=142 142 % 10 = 2 So 81655-71-2 is a valid CAS Registry Number.