The CAS Registry Mumber 63558-03-2 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 6,3,5,5 and 8 respectively; the second part has 2 digits, 0 and 3 respectively. Calculate Digit Verification of CAS Registry Number 63558-03: (7*6)+(6*3)+(5*5)+(4*5)+(3*8)+(2*0)+(1*3)=132 132 % 10 = 2 So 63558-03-2 is a valid CAS Registry Number.