The CAS Registry Mumber 3321-83-3 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,3,2 and 1 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 3321-83: (6*3)+(5*3)+(4*2)+(3*1)+(2*8)+(1*3)=63 63 % 10 = 3 So 3321-83-3 is a valid CAS Registry Number.