The CAS Registry Mumber 4521-88-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 4,5,2 and 1 respectively; the second part has 2 digits, 8 and 8 respectively. Calculate Digit Verification of CAS Registry Number 4521-88: (6*4)+(5*5)+(4*2)+(3*1)+(2*8)+(1*8)=84 84 % 10 = 4 So 4521-88-4 is a valid CAS Registry Number.