The CAS Registry Mumber 180339-31-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,8,0,3,3 and 9 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 180339-31: (8*1)+(7*8)+(6*0)+(5*3)+(4*3)+(3*9)+(2*3)+(1*1)=125 125 % 10 = 5 So 180339-31-5 is a valid CAS Registry Number.