The CAS Registry Mumber 139685-64-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,9,6,8 and 5 respectively; the second part has 2 digits, 6 and 4 respectively. Calculate Digit Verification of CAS Registry Number 139685-64: (8*1)+(7*3)+(6*9)+(5*6)+(4*8)+(3*5)+(2*6)+(1*4)=176 176 % 10 = 6 So 139685-64-6 is a valid CAS Registry Number.