The CAS Registry Mumber 16731-35-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,6,7,3 and 1 respectively; the second part has 2 digits, 3 and 5 respectively. Calculate Digit Verification of CAS Registry Number 16731-35: (7*1)+(6*6)+(5*7)+(4*3)+(3*1)+(2*3)+(1*5)=104 104 % 10 = 4 So 16731-35-4 is a valid CAS Registry Number.