The CAS Registry Mumber 91781-12-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,1,7,8 and 1 respectively; the second part has 2 digits, 1 and 2 respectively. Calculate Digit Verification of CAS Registry Number 91781-12: (7*9)+(6*1)+(5*7)+(4*8)+(3*1)+(2*1)+(1*2)=143 143 % 10 = 3 So 91781-12-3 is a valid CAS Registry Number.