The CAS Registry Mumber 87816-35-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,7,8,1 and 6 respectively; the second part has 2 digits, 3 and 5 respectively. Calculate Digit Verification of CAS Registry Number 87816-35: (7*8)+(6*7)+(5*8)+(4*1)+(3*6)+(2*3)+(1*5)=171 171 % 10 = 1 So 87816-35-1 is a valid CAS Registry Number.