The CAS Registry Mumber 517-40-8 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 5,1 and 7 respectively; the second part has 2 digits, 4 and 0 respectively. Calculate Digit Verification of CAS Registry Number 517-40: (5*5)+(4*1)+(3*7)+(2*4)+(1*0)=58 58 % 10 = 8 So 517-40-8 is a valid CAS Registry Number.