The CAS Registry Mumber 128745-31-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,7,4 and 5 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 128745-31: (8*1)+(7*2)+(6*8)+(5*7)+(4*4)+(3*5)+(2*3)+(1*1)=143 143 % 10 = 3 So 128745-31-3 is a valid CAS Registry Number.