The CAS Registry Mumber 4576-91-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 4,5,7 and 6 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 4576-91: (6*4)+(5*5)+(4*7)+(3*6)+(2*9)+(1*1)=114 114 % 10 = 4 So 4576-91-4 is a valid CAS Registry Number.