The CAS Registry Mumber 80997-81-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,0,9,9 and 7 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 80997-81: (7*8)+(6*0)+(5*9)+(4*9)+(3*7)+(2*8)+(1*1)=175 175 % 10 = 5 So 80997-81-5 is a valid CAS Registry Number.