The CAS Registry Mumber 3191-72-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,1,9 and 1 respectively; the second part has 2 digits, 7 and 2 respectively. Calculate Digit Verification of CAS Registry Number 3191-72: (6*3)+(5*1)+(4*9)+(3*1)+(2*7)+(1*2)=78 78 % 10 = 8 So 3191-72-8 is a valid CAS Registry Number.