The CAS Registry Mumber 71372-91-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,1,3,7 and 2 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 71372-91: (7*7)+(6*1)+(5*3)+(4*7)+(3*2)+(2*9)+(1*1)=123 123 % 10 = 3 So 71372-91-3 is a valid CAS Registry Number.