The CAS Registry Mumber 138691-00-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,8,6,9 and 1 respectively; the second part has 2 digits, 0 and 0 respectively. Calculate Digit Verification of CAS Registry Number 138691-00: (8*1)+(7*3)+(6*8)+(5*6)+(4*9)+(3*1)+(2*0)+(1*0)=146 146 % 10 = 6 So 138691-00-6 is a valid CAS Registry Number.