The CAS Registry Mumber 73313-51-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,3,3,1 and 3 respectively; the second part has 2 digits, 5 and 1 respectively. Calculate Digit Verification of CAS Registry Number 73313-51: (7*7)+(6*3)+(5*3)+(4*1)+(3*3)+(2*5)+(1*1)=106 106 % 10 = 6 So 73313-51-6 is a valid CAS Registry Number.