The CAS Registry Mumber 87281-87-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,7,2,8 and 1 respectively; the second part has 2 digits, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 87281-87: (7*8)+(6*7)+(5*2)+(4*8)+(3*1)+(2*8)+(1*7)=166 166 % 10 = 6 So 87281-87-6 is a valid CAS Registry Number.