The CAS Registry Mumber 1660-87-3 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,6,6 and 0 respectively; the second part has 2 digits, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 1660-87: (6*1)+(5*6)+(4*6)+(3*0)+(2*8)+(1*7)=83 83 % 10 = 3 So 1660-87-3 is a valid CAS Registry Number.