The CAS Registry Mumber 139888-05-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,9,8,8 and 8 respectively; the second part has 2 digits, 0 and 5 respectively. Calculate Digit Verification of CAS Registry Number 139888-05: (8*1)+(7*3)+(6*9)+(5*8)+(4*8)+(3*8)+(2*0)+(1*5)=184 184 % 10 = 4 So 139888-05-4 is a valid CAS Registry Number.