The CAS Registry Mumber 1921-86-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,9,2 and 1 respectively; the second part has 2 digits, 8 and 6 respectively. Calculate Digit Verification of CAS Registry Number 1921-86: (6*1)+(5*9)+(4*2)+(3*1)+(2*8)+(1*6)=84 84 % 10 = 4 So 1921-86-4 is a valid CAS Registry Number.