The CAS Registry Mumber 3363-91-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,3,6 and 3 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 3363-91: (6*3)+(5*3)+(4*6)+(3*3)+(2*9)+(1*1)=85 85 % 10 = 5 So 3363-91-5 is a valid CAS Registry Number.