The CAS Registry Mumber 10306-63-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,0,3,0 and 6 respectively; the second part has 2 digits, 6 and 3 respectively. Calculate Digit Verification of CAS Registry Number 10306-63: (7*1)+(6*0)+(5*3)+(4*0)+(3*6)+(2*6)+(1*3)=55 55 % 10 = 5 So 10306-63-5 is a valid CAS Registry Number.