The CAS Registry Mumber 77603-03-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,7,6,0 and 3 respectively; the second part has 2 digits, 0 and 3 respectively. Calculate Digit Verification of CAS Registry Number 77603-03: (7*7)+(6*7)+(5*6)+(4*0)+(3*3)+(2*0)+(1*3)=133 133 % 10 = 3 So 77603-03-3 is a valid CAS Registry Number.