The CAS Registry Mumber 4521-39-5 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, 3 and 9 respectively. Calculate Digit Verification of CAS Registry Number 4521-39: (6*4)+(5*5)+(4*2)+(3*1)+(2*3)+(1*9)=75 75 % 10 = 5 So 4521-39-5 is a valid CAS Registry Number.