The CAS Registry Mumber 97800-81-2 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,7,8,0 and 0 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 97800-81: (7*9)+(6*7)+(5*8)+(4*0)+(3*0)+(2*8)+(1*1)=162 162 % 10 = 2 So 97800-81-2 is a valid CAS Registry Number.