The CAS Registry Mumber 1870-16-2 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,8,7 and 0 respectively; the second part has 2 digits, 1 and 6 respectively. Calculate Digit Verification of CAS Registry Number 1870-16: (6*1)+(5*8)+(4*7)+(3*0)+(2*1)+(1*6)=82 82 % 10 = 2 So 1870-16-2 is a valid CAS Registry Number.