The CAS Registry Mumber 5639-01-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,6,3 and 9 respectively; the second part has 2 digits, 0 and 1 respectively. Calculate Digit Verification of CAS Registry Number 5639-01: (6*5)+(5*6)+(4*3)+(3*9)+(2*0)+(1*1)=100 100 % 10 = 0 So 5639-01-0 is a valid CAS Registry Number.