The CAS Registry Mumber 138858-51-2 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,8,8,5 and 8 respectively; the second part has 2 digits, 5 and 1 respectively. Calculate Digit Verification of CAS Registry Number 138858-51: (8*1)+(7*3)+(6*8)+(5*8)+(4*5)+(3*8)+(2*5)+(1*1)=172 172 % 10 = 2 So 138858-51-2 is a valid CAS Registry Number.