The CAS Registry Mumber 57391-97-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,7,3,9 and 1 respectively; the second part has 2 digits, 9 and 7 respectively. Calculate Digit Verification of CAS Registry Number 57391-97: (7*5)+(6*7)+(5*3)+(4*9)+(3*1)+(2*9)+(1*7)=156 156 % 10 = 6 So 57391-97-6 is a valid CAS Registry Number.