The CAS Registry Mumber 73318-31-7 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 8 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 73318-31: (7*7)+(6*3)+(5*3)+(4*1)+(3*8)+(2*3)+(1*1)=117 117 % 10 = 7 So 73318-31-7 is a valid CAS Registry Number.