The CAS Registry Mumber 71539-97-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,1,5,3 and 9 respectively; the second part has 2 digits, 9 and 7 respectively. Calculate Digit Verification of CAS Registry Number 71539-97: (7*7)+(6*1)+(5*5)+(4*3)+(3*9)+(2*9)+(1*7)=144 144 % 10 = 4 So 71539-97-4 is a valid CAS Registry Number.