The CAS Registry Mumber 41217-20-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 4,1,2,1 and 7 respectively; the second part has 2 digits, 2 and 0 respectively. Calculate Digit Verification of CAS Registry Number 41217-20: (7*4)+(6*1)+(5*2)+(4*1)+(3*7)+(2*2)+(1*0)=73 73 % 10 = 3 So 41217-20-3 is a valid CAS Registry Number.