The CAS Registry Mumber 64753-91-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 6,4,7,5 and 3 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 64753-91: (7*6)+(6*4)+(5*7)+(4*5)+(3*3)+(2*9)+(1*1)=149 149 % 10 = 9 So 64753-91-9 is a valid CAS Registry Number.