The CAS Registry Mumber 53555-06-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,3,5,5 and 5 respectively; the second part has 2 digits, 0 and 6 respectively. Calculate Digit Verification of CAS Registry Number 53555-06: (7*5)+(6*3)+(5*5)+(4*5)+(3*5)+(2*0)+(1*6)=119 119 % 10 = 9 So 53555-06-9 is a valid CAS Registry Number.