The CAS Registry Mumber 5103-65-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,1,0 and 3 respectively; the second part has 2 digits, 6 and 5 respectively. Calculate Digit Verification of CAS Registry Number 5103-65: (6*5)+(5*1)+(4*0)+(3*3)+(2*6)+(1*5)=61 61 % 10 = 1 So 5103-65-1 is a valid CAS Registry Number.