The CAS Registry Mumber 395639-53-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 3,9,5,6,3 and 9 respectively; the second part has 2 digits, 5 and 3 respectively. Calculate Digit Verification of CAS Registry Number 395639-53: (8*3)+(7*9)+(6*5)+(5*6)+(4*3)+(3*9)+(2*5)+(1*3)=199 199 % 10 = 9 So 395639-53-9 is a valid CAS Registry Number.