The CAS Registry Mumber 2717-03-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,7,1 and 7 respectively; the second part has 2 digits, 0 and 3 respectively. Calculate Digit Verification of CAS Registry Number 2717-03: (6*2)+(5*7)+(4*1)+(3*7)+(2*0)+(1*3)=75 75 % 10 = 5 So 2717-03-5 is a valid CAS Registry Number.