The CAS Registry Mumber 335203-33-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 3,3,5,2,0 and 3 respectively; the second part has 2 digits, 3 and 3 respectively. Calculate Digit Verification of CAS Registry Number 335203-33: (8*3)+(7*3)+(6*5)+(5*2)+(4*0)+(3*3)+(2*3)+(1*3)=103 103 % 10 = 3 So 335203-33-3 is a valid CAS Registry Number.