The CAS Registry Mumber 95639-09-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,5,6,3 and 9 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 95639-09: (7*9)+(6*5)+(5*6)+(4*3)+(3*9)+(2*0)+(1*9)=171 171 % 10 = 1 So 95639-09-1 is a valid CAS Registry Number.