The CAS Registry Mumber 5172-57-6 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,1,7 and 2 respectively; the second part has 2 digits, 5 and 7 respectively. Calculate Digit Verification of CAS Registry Number 5172-57: (6*5)+(5*1)+(4*7)+(3*2)+(2*5)+(1*7)=86 86 % 10 = 6 So 5172-57-6 is a valid CAS Registry Number.