The CAS Registry Mumber 13420-71-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,3,4,2 and 0 respectively; the second part has 2 digits, 7 and 1 respectively. Calculate Digit Verification of CAS Registry Number 13420-71: (7*1)+(6*3)+(5*4)+(4*2)+(3*0)+(2*7)+(1*1)=68 68 % 10 = 8 So 13420-71-8 is a valid CAS Registry Number.