The CAS Registry Mumber 75521-96-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,5,5,2 and 1 respectively; the second part has 2 digits, 9 and 6 respectively. Calculate Digit Verification of CAS Registry Number 75521-96: (7*7)+(6*5)+(5*5)+(4*2)+(3*1)+(2*9)+(1*6)=139 139 % 10 = 9 So 75521-96-9 is a valid CAS Registry Number.